The offside rule, explained: when a player is (and isn’t) offside
Offside in one sentence, the conditions that must all be true, and the situations where you are never offside — with the active-vs-passive distinction that trips people up.
The rule in one sentence
A player is caught offside if, at the moment a teammate plays the ball, they are in the opponents’ half and closer to the opponents’ goal line than both the ball and the second-to-last opponent — and then get involved in the play. That last clause matters: being in an offside position is not, by itself, an offence.
The three things that must all be true
For an offside offence to be called, all of these have to hold at the instant the ball is played by a teammate: the player is in the opponents’ half; they are ahead of the ball; and they are ahead of the second-to-last opponent (usually the last outfield defender, because the goalkeeper is often the last of the two). Miss any one, and it is not offside.
When you are NOT offside
You cannot be offside in your own half. You are onside if you are level with the second-to-last opponent, or level with the last two opponents. And you are never offside directly from a goal kick, a throw-in or a corner — a detail that surprises a lot of newer fans.
Active vs passive: the part people miss
Standing in an offside position is only punished if the player then interferes with play (touches the ball), interferes with an opponent (blocks the line of sight or challenges for it), or gains an advantage (plays a ball that rebounded off the post or a defender). A player in an offside position who stays out of it — passive — is left alone until they get involved.
A quick worked example
A striker stands a yard beyond the last defender as the pass is played — offside position. If the ball runs to them and they shoot, it is offside. If instead a teammate onside collects it and the striker never touches it or obstructs anyone, play goes on. Same starting position, different outcome, decided entirely by involvement. Note too that arms and hands are not counted when judging the position — only the head, body and feet.