The Red attacker No. 8 receives the ball from his team-mate No. 7. 

The Red attacker No. 8  is offside since he is nearer to his opponents' goal line than both the ball and the second last opponent No. 2. 
The Red attacker No. 8 therefore interferes with play by playing (or touching) the ball.

The Red attacker No. 8 receives the ball from his team-mate No. 7. 

The Red attacker No. 8 is not offside, because when the ball was played to him by his team-mate No. 7, he was level with the second last defender No. 3.

The Red attacker No. 8 is not offside, because when the ball was played to him by his team-mate No. 7, he was level with the second last defender No. 3.

(In other words, Red attacker No. 8 was not nearer to his opponents' goal line, than both the ball and the second last defender No. 3 - when the ball was played to him by Red attacker No. 7.)

The Red attacker No. 8 is in an offside position, because he was nearer to his opponents' goal line, than both the ball and the second last defender No. 2 - when the ball was originally played to him by Red attacker No. 7.
Red attacker No. 8 is also interfering with an opponent (the goalkeeper No.1) by clearly obstructing the goalkeeper's line of vision and movement. This distracts the goalkeeper.

The Red attacker No. 8 is in an offside position, because he was nearer to his opponents' goal line, than both the ball and the second last defender No. 4 - when the ball was originally played to him by Red attacker No. 7.

The prostrate Red attacker No. 8 is also interfering with an opponent by obstructing the goalkeeper's movement (he distracts the goalkeeper). 

The Red attacker No. 8 is lying near the goal area in an offside position; but he is not involved in active play. He is not distracting the goalkeeper's movement, nor is he obstructing the goalkeeper's line of view. The Red attacker No. 8 should therefore not be penalised.

Although the Red attacker No. 8 is in an offside position when the ball is kicked towards the goal by his team-mate No. 7, he is not penalised, because he is not involved in active play.
He is not interfering with an opponent and he is not interfering with play. And he does not gain an advantage by being in that position.

The shot by the Red attacker No. 7 rebounds from the goalpost to a team-mate No. 8 who was in an offside position when the ball was originally kicked. 

Red attacker No. 8 has gained an advantage by playing a ball that rebounds to him off a goalpost (or the crossbar) having originally been in an offside position. 

The shot by the Red attacker No. 7 rebounds from the goalkeeper to a team-mate No. 8 who was in an offside position when the ball was originally kicked. 

Red attacker No. 8 has gained an advantage by playing a ball that rebounds to him off an opponent (the goalkeeper) having originally been in an offside position. 

A - the ball is kicked to the goalkeeper by the Yellow defending team-mate No. 2.
B - The goalkeeper No.1 kicks the ball upfield whilst the attacking Red player No. 7 turns to run back towards the halfway line to take up an onside position.
C - The ball is intercepted by an onside attacking Red team-mate (No. 8), who then passes the ball to onside team-mate No. 9 on the right wing. 

The Red attacker No. 7 is not penalised for being in an offside position, because he is not involved in active play,

Terminology:

The diagram shows an attacker (the dark figure), alongside the second last defender (the white figure). The dotted line depicts the offside line in relation to the second last defender.

In the definition of offside position, "nearer to his opponent" goal line means that any part of his head, body or feet is nearer to his opponents' goal line than both the ball and the second last opponent. The arms are not included in this definition.

When deciding whether or not an attacker is nearer to the opponent's goal line than the second last defender, consideration should only be given to those parts of the body that can legally be used to play the ball. Hands and arms should therefore be ignored when calculating offside. The diagram shows that it is possible for the attacker to play the ball ahead of the dotted offside line with (a) the head, (b) or the foot/leg, (c) or the torso.

13.

It is not an offence in itself to be in an offside position. 

A player in an offside position will only be penalised if in the opinion of the Referee he is involved with active play by:
(a) interfering with play or
(b) interfering with an opponent or
(c) gaining an advantage by being in that position.

The 2 diagrams show the offside Red attacker No. 8 in very close proximity to the goalkeeper. This distraction have an effect on the concentration of the goalkeeper if he needs to make a save. 

The Red attacker No. 8 is nearer to his opponents' goal line than both the ball and the second last opponent. The Red attacker No. 8 is therefore, in an offside position and interfering with an opponent.

16a.

Shall the Referee allow the goal?

Referees have been known to stop play before the ball reaches position 'd', on the assumption that the ball will reach the Red attacker No. 9. 
As it is not an offence to be in an offside position, the Referee should wait to see if the  Red attacker No. 9 becomes involved with active play - or not!

If the ball is accidentally knocked (at position 'd') into the goal by the Yellow defender No. 3, the goal may be allowed - in the opinion of the referee. Why? 
The Referee decides whether the Red attacker No. 9 is involved in active play or not. 
If the Referee feels that the Red attacker No. 9 has has made a gesture or movement which deceives or distracts the goal keeper, then the goal will be disallowed. 
If the Referee feels that the Red attacker No. 9 did not interfere with play, and he did not interfere with the goalkeeper, and he did not gain an advantage by being in that position, then the goal is legal.
This is a good example of why Law 11 states that offside is "in the opinion of the Referee".

To be in an offside position, the Red attacker No. 9 must be located nearer to his opponents' goal line than both the ball (line 'b') and the second last defender (line 'a'). 

Although the Red attacker No. 9 is standing in an offside position, he will only be penalised if in the opinion of the Referee he is involved in active play by:

(a) interfering with play or
(b) interfering with an opponent or
(c) gaining an advantage by being in that position

17.

It is not an offence in itself to be in an offside position. 

The Red attacker No. 8 receives the ball from his team-mate No. 7. 

The Red attacker No. 8  is offside since he is nearer to his opponents' goal line than both the ball and the second last opponent No. 2. 

The Red attacker No. 8 therefore interferes with play by playing or touching the ball.

The Red attacker No. 6  is in an offside position  since he is nearer to his opponents' goal line than both the ball and the second last opponent No. 2. 

The Red attacker No. 6 interferes with play by touching the ball. The goal is disallowed.

It is not an offence in itself to be in an offside position. 

18b

NO. 8 IS OFFSIDE

Gaining an advantage by being in that position means playing a ball that rebounds to him off a post or the crossbar having been in an offside position or playing a ball that rebounds to him off an opponent having been in an offside position.

Gained an advantage.

Fig. 18b is the same original situation as shown in Fig 18a above; but if after the Red attacker No. 7 shoots the ball towards the defenders' goal, the ball deflects off defending player No. 2, and goes to the Red attacker No. 8 who is standing near the right wing touchline, the Red attacker No. 8 must be penalised for being offside. At the moment that the ball was shot towards the goal by the Red attacker No. 7, the Red attacker No. 8 was in an offside position. The Red attacker No. 8 is deemed to have gained an advantage by being in that position and he becomes involved with active play when he receives the ball after it has rebounded off defender No. 2. 
A second phase of play cannot be said to have started if the ball rebounds off the defender. (See below *)

The Yellow defender No. 2 passes the ball back towards his Yellow team goalkeeper No. 1. The Red attacker No. 7 is standing in an offside position because he is nearer to his opponents' goal line than both the ball and the second last defender No. 3. The Red attacker No. 7 intercepts the ball and scores a goal. The goal should be allowed to count, because no offside infringement had occurred.

Attacker No. 7 passes the ball forwards for attacker No. 9 to chase. Attacker No. 8 who is standing in an offside position on the field of play near the touchline, steps off the field of play, thus indicating to the Referee that he does not wish to be involved with active play during this phase of the game. Attacker No. 9 runs forwards and gains possession of the ball. Attacker No. 8 should not be penalised, as he is not interfering with play.

20a.

Defender No. 4 should be cautioned for unsporting behaviour once the phase of play has completed, and the ball has gone out of play.

Attacker No. 7 passes the ball forwards for attacker No. 8. Just before the pass is made, the second last defender No. 4 was standing inside the field of play, but deliberately moves off the field of play in an attempt to place Red attacker No. 8 in an offside position.  This manoeuvre (trick) by the defender No. 4 is an attempt to circumvent the spirit of the Offside Law 11.  The Referee should assume that the defender No. 4 is ON the field of play in this situation. Thus, the Red attacker No. 8 in not in an offside position, and play should be allowed to continue. 

Italy's defender Christian Panucci (No. 2), who had been injured seconds earlier, was lying behind the goal when the Holland striker Ruud van Nistelrooy (No. 9) scored.

When Italy's goalkeeper (No.1) fisted out a free kick shot near his right hand goal post, he accidentally knocked down his own player Christian Panucci (No. 2) onto the ground and behind the goal line. The fisted ball travelled back out to Holland's free-kick-taker Rafael van der Vaart No. 23, who re-struck the ball back towards the goal, and Ruud van Nistelrooy (No. 9) stabbed the ball into the goal. 

Even though Panucci (No. 2) had fallen off the field of play, his position was still relevant for the purposes of the offside law and he is still considered part of the game. A defender is in play, unless he has permission to be off the field. This is a widely known interpretation of the offside law among referees, but is not generally known by the wider footballing public, and indeed many people in football. Without this interpretation, what could happen is the defending team (including the goalkeeper) could step off the field, to play attacking players offside, and that is clearly unacceptable. Unless a defending player has permission from the referee to be off the field of play, he is deemed to be on it and therefore part of the game. That is why Panucci (No. 2) the Italian defender, even though his momentum had taken him off the field of play, was still deemed to be part of the game.  (David Taylor, the UEFA general secretary.)

When the ball was re-struck by Holland's Rafael van der Vaart No. 23, Christian Panucci (No. 2) was off the field, and only Holland's goalkeeper (No. 1) was closer to the goal line than Ruud van Nistelrooy (No. 9). Even so, in terms of judging offside, Panucci (No. 2) , who slid off the field, was still regarded as active and considered part of the game; even though he was accidentally knocked off the field of play through contact with his own goalkeeper. 

Red attacker No. 7 passes the ball forwards for onside attacker No. 9 to run on to. Red attacker No. 8 who is standing in an offside position indicates to the Referee (by raising his arms into the air) that he does not wish to be involved with active play during this phase of the game.  

Onside Red attacker No. 9 runs forwards and legally gains possession of the ball. 

Attacker No. 8 has indicated that he does not wish to be involved in this move. He is not interfering with play, and neither is he interfering with an opponent.

Offside occurs AT THE MOMENT THE BALL IS PLAYED by a team-mate.
Red attacker No. 7 passes the ball forwards for attacker No. 8 to chase. At the exact moment when the pass was made,  the Red attacker No. 8 was standing in an ONside position (in other words, Red attacker No. 8 was not nearer to his opponents' goal line, than both the ball and the second last defender - when the ball was played by Red attacker No. 7.) As soon as the pass is made, Red attacker No. 8 can run forwards beyond the second last defender, and attempt to gain possession of the ball without fear of being penalised for offside.

Red attacker No. 7 passes the ball towards the penalty mark for Red attacker No. 9 to chase. When the pass is made, Red attacker No. 9 is at position 'a' and is NOT OFFSIDE.
The ball accidentally deflects off the onside Red attacker No. 8 at the precise moment that Red attacker No. 9 reaches the new position 'b'.
Red attacker No. 9 is now OFFSIDE at the new position 'b', because he was nearer to his opponents' goal line than both the ball and the second last opponent at the precise moment that the ball last 'touched' his team-mate Red attacker No. 8. Thus becoming involved in active play by interfering with play by touching the ball at position 'b'.

23a.

Even though the Red attacker No. 8 is walking back towards the halfway line when this move takes place, and may have indicated to the Referee that he does not want to get involved with active play, he is still interfering with play, because the ball 'touches' him whilst he is in an offside position. 

It makes no difference whether the touch by Red attacker No. 8 is accidental or done on purpose.  The word 'touches' in the offside Law is not governed by whether the touch is accidental or done on purpose.

The answer to this scenario, is that although Red attacker No. 9 remains in an onside position, the Referee should penalise Red attacker No. 8 for interfering with play by touching the ball whilst being in an offside position. 

Red attacker No. 7 passes the ball towards the penalty mark for Red attacker No. 9 to chase. When the pass is made, Red attacker No. 9 is at position 'a' and NOT OFFSIDE. And Red attacker No. 8 who is in in offside position has indicated to the Referee that he does not want to get involved with active play.
The ball accidentally rebounds off the offside Red attacker No. 8 at the precise moment that Red attacker No. 9 reaches the new position 'b'. Red attacker No. 9 has always remained behind the ball whilst making his run towards position 'b' and is therefore always ONSIDE because he remained further from his opponents' goal line than the ball.
Red attacker No. 8 is in an  offside position because he was nearer to his opponents' goal line than both the ball and the second last opponent at the precise moment when the ball was passed towards the penalty spot by  team-mate Red attacker No. 7. Thus, Red attacker No. 8 inadvertently becomes involved in active play by interfering with play (by touching the ball).

Red attacker No. 7 takes a corner kick and passes the ball to his colleague Red attacker No. 8 who stops the ball with his foot. Red attacker No. 7 then moves from position 'a' to 'b' where he plays the ball. At the precise moment when the Red attacker No. 8 stopped (touched) the ball, Red attacker No. 7 was in an offside position 'a', and therefore nearer to his opponents' goal line than both the ball and the second last opponent. And by moving from position 'a' to 'b', the Red attacker No. 7 had interfered with play by touching the ball and involving himself in active play.

25. NOT nearer to opponents' goal line.

All of the Red attackers remain behind the ball. The most advanced Red attacker No. 7 shoots the ball towards goal, the  goalkeeper parries it into the path of the Red attacker No. 9 who shots and scores a goal.  

At the moment when the Red attacker No. 7 shoots the ball towards goal, all of the Red attacker (No. 7, No. 8, & No. 9) are NOT in an offside position; because although they are nearer to their opponents' goal line than the second last defender, they are NOT nearer to their opponents' goal line than both the ball AND the second last opponent. The goal is legal.

Phase 1: Red attacker No. 7 passes the ball towards the penalty mark for Red attacker No. 8 to run onto. When the pass is made, Red attacker No. 8 is at position 'a' and NOT OFFSIDE. Red attacker No. 8 runs and collects the ball near the penalty mark at position 'b'. Red attacker No. 9 who is in an offside position is not involved with active play. Phase 1 ceases, and the move into Phase 2 (see below) is therefore allowed to proceed by the Referee (because no offside infringement has occurred).

When the Red attacker No. 7 reaches his position 'b', Red attacker No. 9 also reaches his position 'b' and he is still in an offside position. 

When Red attacker No. 7 reaches his position 'c', Red attacker No. 9 also reaches his position 'c' and becomes ONside because he is not nearer to the opponent's goal line than the ball. 

If the Red attacker No. 7 now passes the ball from position 'c' to the Red attacker No. 9 in position 'c', there is no offside infringement, because Red attacker No. 9 is now ONside (i.e.  he is NOT nearer to his opponents' goal line than both the ball AND the second last opponent.)

Phases of play.  The following 2 phases of play occurred in the Euro 2004 game. Czech Republic v Holland. Holland's front attacker Van Nistelrooy (Red No. 9 in the diagrams below) who was wandering back in the centre of the field from an offside position (in phase 1), was subsequently played onside by the movement of his right wing colleague Robben (Red No. 8). Van Nistelrooy (Red No. 9) eventually receives the ball from Robben before going on to score a goal (in phase 2).

Van Nistelrooy (Red No. 9) is in an offside position near to the goalkeeper No.1, and is slowly making his way back towards the halfway line. He is not involved in the active play of phase one, and he is not interfering with an opponent or with play.

Phase 1 of play ends as soon as Van Nistelrooy's colleague (Red No. 8) on the right wing (Robben) who is running with the ball at his feet, reaches a position that is level with Van Nistelrooy. 

At this moment, Van Nistelrooy becomes ONside. Phase one ends, and phase two begins.
When Robben (Red No. 8)  subsequently passes the ball from the left wing to Van Nistelrooy (Red No. 9), Van Nistelrooy is behind the ball (dotted line) and therefore he is no longer in an offside position.

When the play action reaches phase 2, the question of whether Van Nistelrooy (Red No. 9) is offside or not, is effectively reset, and the offside calculation begins afresh.  Van Nistelrooy, is no longer in an offside position, and completes the move by scoring a perfectly legitimate goal.

27.

Scenario: Red attacking players No. 6, No.7 who is in control of the ball, and No. 8 run from respective onside positions 'a' to positions 'b', and No. 7 kicks the ball into the goal.  At the precise moment that the Red attacker No. 7 reaches position ' b ' and kicks the ball towards the goal, Red attacking players numbers 6, and 8 are standing in offside positions. (Because they are nearer to the opponents' goal line, than both the ball and the second last opponent when the ball is kicked by team-mate No. 7).
The first sentence of Law 11 (Offside) states: "It is not an offence in itself to be in an offside position."

Should the gaol be allowed to count?

If in the opinion of the Referee, Red attacker No. 6, or Red attacker No. 8 are involved in active play by: (a) interfering with play, (b) interfering with an opponent, or (c) gaining an advantage by being in that position - the Referee will penalise them and award an indirect free kick to the defending team. 
In diagram No. 27, Red attacking players No, 6, & 8 are not "interfering with an opponent". (In other words, they are not preventing an opponent from playing or being able to play the ball. And neither are they clearly obstructing the goalkeeper’s line of vision or movements. They are also not making any gestures or movement while standing in the path of the ball to deceive or distract an opponent.). They are also not "interfering with play" (In other words, none of them plays or touches the ball kicked by their team-mate No. 7.) Finally - Red attacking players No, 6, & 8 have not gained an advantage by being in position 'b'.
Therefore, they have not infringed any of the Law 11 rulings. The goal should be allowed to stand.

Red attacker No. 9 having been in the offside position 'a', cannot make himself onside by running into the onside position 'b' and then back into an offside position 'c' before he touches the ball.
Red attacker No. 9 who is in the offside position 'a' at the moment the ball is played by Red attacking team-mate No. 8, can become "onside" if:
(1) He is not in front of the ball when it is next played by one of his team.
(2) The positions of the opponents change so Red attacker No. 9 is no longer in an offside position when the ball is next played by one of his team.
(3) An opponent intentionally plays, controls or gains possession of the ball.
(4) The ball goes out of play.

The Red attacker No. 9 involves himself with active play by interfering with play (i.e. he plays the ball passed by team-mate Red No. 8) whilst originally being in an offside position. He should therefore be penalised. 

When the Red attacker No. 8, kicks the ball towards position 'b', Red attacker No. 9 is at offside position 'a' inside the opponent's half.

The Red attacker No. 9 cannot make himself onside by running to intercept the ball inside his own half at position 'b'. Offside is judged at the precise moment that the ball was played by the Red attacker No. 8. Offside is not judged at the moment that an offside  player touches the ball.

Fig. 30a

It is not an offence to be in an offside position.

If Red attacker No. 8 decides to stay where he is, and does not become involved with active play, he should not be penalised for being in an offside position, and play should be allowed to continue. 

Fig 30b.

Red attacker No. 8 is in an OFFSIDE position, and will be penalised if he makes his way to position 'Y' and interferes with play by touching or playing the ball.

By moving towards the ball from an offside position after the ball was played by his team-mate, the Red attacker No. 8 involves himself in active play by interfering with play (i.e. he touches or plays the ball at position 'Y').

Fig 30c:

Red attacker No. 8 is NOT OFFSIDE

In other words, Red attacker No. 8 was in line with Red attacker No. 9 and the ball, (i.e. NOT nearer to his opponents' goal line than the ball). Red attacker No. 8 is therefore entitled to become involved in active play by interfering with play, and can legally move to gain possession of the ball at position 'Y', or at any other position that the ball may have been played to by Red attacker No 9.

Fig. 30d

Red attacker No. 8 is NOT OFFSIDE

In other words, Red attacker No. 8 was behind the ball, (i.e. NOT nearer to his opponents' goal line than the ball). Red attacker No. 8 is therefore entitled to become involved in active play by interfering with play, and can legally move to gain possession of the ball at position 'Y', or at any other position that the ball may have been played to by Red attacker No 9.

Fig. 31a

Red attacker No. 8 is NOT OFFSIDE
 If a defender (e.g. player No.2 above) deliberately leaves the field of play, the Referee must now consider the location of that defender when deciding if an attacker (e.g. No.9) is in an offside position or not?

Red attacker No.9 is not in an offside position because (introduced in 2009-2010) any defending player leaving the field of play for any reason without the referee's permission shall be considered to be on his own goal line or touchline for the purposes of offside until the next stoppage in play. If the Referee believes that the Yellow defender No.2 deliberately left the field of play, he should be cautioned when the ball is next out of play .

Note: A defender who leaves the field of play without the Referee's permission is deemed to be on the goal line or touchline nearest to where he left the field of play, and should therefore be considered as though he was still on the field of play. A defender who has left the field of play with the referee’s permission is not included in determining where the last and second to last defenders are located.