An attacker is offside if part of their head, body, or feet that can legally play the ball is closer to the opponent's goal line than both the ball and the second-to-last defender — at the exact moment a teammate plays the ball forward — and they then become involved in the play.

The 30-second version

Three things have to happen for offside to be called:

1. The attacker is in an offside position when the ball is played by a teammate.
2. The ball is played forward to them or near them.
3. They become involved — by touching the ball, blocking a defender, or interfering with the goalkeeper.

If any one of those is missing, no offside.

How to actually see it on TV

Picture a line drawn across the field where the second-to-last defender stands at the moment the pass is kicked. (The last defender is almost always the goalkeeper, so practically that means "the last outfield defender.") If the attacker is past that line when the pass is played, they're in an offside position.

Two important details:

• It's the position at the moment of the pass, not at the moment they receive it. Attackers often time runs to be onside when the pass is struck and onside when they get the ball — but the only frame that matters is when the kicker's foot meets the ball.
• Hands and arms don't count. Only parts of the body that can legally play the ball — head, torso, legs, feet.

A simple example

Striker stands 3 yards behind the last defender. A midfielder takes a touch and plays the ball forward. The striker sprints onto it and scores.

Onside. Goal stands. The striker was behind the defender when the ball was played.

Now run it back: same play, but the striker is 1 yard ahead of the last defender when the midfielder kicks the pass. He's quicker than the defender and arrives at the ball first.

Offside. No goal. He was past the second-to-last defender at the moment of the pass — even by an inch.

What fans usually get wrong

• "He was onside, the goalie came out!" — The goalkeeper counts as one of the last two defenders. If the keeper is up the field, the second-to-last defender becomes the deepest outfield player. The line moves accordingly.
• "He was even with him!" — A player level with the second-to-last defender is onside. Offside requires being clearly past them.
• "He's offside, look where he is!" — Being in an offside position is not an offence by itself. The attacker has to actually become involved in the play. A striker standing offside on the far post while a teammate scores from the other side is fine, as long as he doesn't interfere.
• "VAR drew the lines wrong" — VAR uses calibrated camera lines synced to the moment of the kick. Margins are tight (often centimeters), but the standard is the same as it's always been.

Active involvement: when offside position becomes an offence

Three ways an offside-positioned attacker becomes involved:

• Interfering with play — touches the ball, or makes a clear attempt to play it.
• Interfering with an opponent — blocks the keeper's line of sight, challenges for the ball, or makes an obvious action that affects a defender's ability to play.
• Gaining an advantage — the ball rebounds off the post, crossbar, or a defender, and the offside-positioned attacker plays it.

If none of those happen, the attacker is "in an offside position" but not offside in a punishable sense.

Restart

When offside is called, the defending team gets an indirect free kick at the spot where the offside player was when the ball was played to them.

Official rule basis

The offside rule is Law 11 in the IFAB Laws of the Game, which FIFA adopts for all official competitions including the World Cup. The current wording was clarified in the 2023 update to specify that the part of the body that can play the ball is what matters — meaning a forward's arm being ahead of the defender no longer makes them offside.