[Bagor]

Whether you feel it's unfair or not, by the letter of the law it's a good goal.

He's not interfering with anyone.

The source of most confusion is clearly in the definition of 'active'. Pundits keep falling back on the dictionary definition of the word, or their own version of it, rather than the one set out in the laws. It's intensely frustrating to see them spreading misinformation - misinformation that leads to the sort of abuse that drives officials out of the game.To be clear, the definition, in the laws, is this: in deciding whether to flag, assistants must watch out for three things, any one of which would make an offside player active.
First, is the offside player interfering with play? As advised by the IFAB since 2005, that means playing or touching the ball. Attempting to play the ball does not count - he must actually play or touch it.
Second, is the player interfering with an opponent's ability to play the ball, by clearly obstructing the opponent's line of vision or movements, or by making a gesture or movement which, in the opinion of the referee, deceives or distracts an opponent?
And third, is the player 'gaining an advantage'? This last point is specific, and is not what Match of the Day seem to think it is. It applies only to an offside player playing a ball that rebounds to him from an opponent, the post or the crossbar. If he does not play the ball from the rebound, then he is not penalised for being in that offside position. Nothing else counts as 'gaining'.
And that's it. If a player ticks any one of those three boxes, he is offside. The three-part definition is remembered as 'PIG' - if a player doesn't Play, Interfere or Gain, he is fine.

http://www.guardian.co.uk/sport/2008...tball.comment3