Where should the Assistant Referee place himself to judge for offside in the following instances?
(a) An defender's momentum, takes him out over the goal line where he remains injured off the field of play.
Answer (a): A player leaving the field during play because of his momentum, is not deemed to have left without the Referee's permission and can therefore re-enter without the Referee's permission. However, this player is clearly injured, awaiting treatment off the field of play. He should be deemed to have left the field of play and will require the Referee's permission to re-enter after he has received treatment. As the injured player is off the field of play, he should not be considered in any offside decisions. The Assistant Referee should move up field in line with the next second last defender remaining on the field of play. The injured player should be discounted when deciding offside in this scenario.
On occasions like this, the Referee will need to decide when a player is genuinely injured (or not!). There will probably be no time for the Referee to actually give permission for this player to be treated - because he will be concentrating closely on the ensuing match action. The Referee will need to decide if the player is genuinely injured, or if he is feigning an injury in the hope that an offside will be given against an opponent. It is a very difficult decision for the Referee to make whilst primarily concentrating on the match action.
(b) An defender's momentum, takes him out over the goal line but he is not injured.
Answer (b): A player leaving the field of play because of his momentum during play, is not deemed to have left without the Referee's permission and can therefore re-enter without the Referee's permission. In this instance, although the defender is off the field of play, (and until he returns to the field of play), he should be deemed to be standing on the goal-line (in the field of play) when considering offside. The Assistant Referee should stand in line with the last opponent on the field of play (which in this case will probably be the defending goalkeeper). When deciding offside in this scenario, the two last defending opponents are the defender who has travelled off the field of play, and the defending player who is nearest to the goal line on the field of play (which in all probability will be the goalkeeper).
If an uninjured defender purposefully remains off the field in an attempt to place an attacker in an offside position, then that defender should also be deemed to be standing on the goal-line (on the field of play) when considering offside. Trickery of this nature circumvents the spirit of the offside Law.