What is Offside in Football?
The rule preventing attackers from goal-hanging: a player is penalised if they are nearer to the opponents' goal than both the ball and the second-last defender when a teammate plays the ball to them, and they get involved in play. Being level with the last outfield defender is onside, and there's no offside from throw-ins, corners, or goal kicks.
Example: The flag stayed down because the striker was level with the last defender when the through ball was played.