I don't think the above definition of 'offside' is quite correct. There are various exceptions, as follows:

  • A player cannot be offside if he is in his own half of the pitch when the ball is passed towards him.

  • A player who isn't considered (at the discretion of the officials) to be 'active' can't be offside. For example if he's running back towards his own goal, or lying down with a broken leg.

  • Sometimes people are offside even when the player with the ball just dribbles the ball and never passes it to the offside player.

  • If the pass is a backpass (a pass towards the player's own goal) then the player is never offside, as in the following diagram.

         O                            X. --+
                                        O  | target
                          O                |  goal
                                     X     |

Put all that into a single sentence and you definitely wouldn't win any awards from the Plain English Campaign.

It has been pointed out to me that FIFA have the official version of the rule here: http://www.fifa2.com/scripts/runisa.dll?s7.131714:GP::67173+refs/laws/law11