High Quality Content by WIKIPEDIA articles! Offside is a law in football which states that if a player is in an offside position when the ball is touched or played by a teammate, he may not become actively involved in the play. A player is in an offside position if he is closer to the opponent`s goal line than both the ball and the second-to-last defender (which is usually the last outfield player), but only if the player is on his opponent`s half of the pitch. "Offside position" is a matter of fact, whereas committing an "offside offence" occurs when the a player is "actively involved" which is subject to the interpretation of the referee. Goals scored after committing an offside offence are nullified if caught by the referee.