How does the offside rule actually work in football?

The offside rule has three parts that all need to be true at once. (1) Position: the attacker is in the opponent's half AND closer to the goal line than the ball AND closer than the second-to-last defender (usually a defender, plus the goalkeeper). (2) Active involvement: the attacker actually plays the ball, interferes with a defender, or gains an advantage from being in that position. (3) The infraction is judged at the moment the ball is played by the attacker's teammate — not when the attacker receives it.

Things that are NOT offside: receiving the ball directly from a goal kick, throw-in or corner kick. Receiving the ball from an opponent's deliberate pass or save (not a deflection). Being level with the second-to-last defender at the moment the ball is played — level is onside, by the laws.

What VAR + semi-automated offside check: not whether the attacker is interfering (that's still subjective and on the on-field referee) but whether the position was offside at the moment the pass was played. The Trionda ball's sensor pins the exact pass moment to the millisecond; the AI limb-tracking from multiple cameras builds a 3D skeleton of every player at that frame. If any part of the attacker's body that can legally score is ahead of the second-to-last defender, it's offside.

Common myths busted: hand/arm offside doesn't exist (you can't score with your hand, so it doesn't count for offside either). And the 'daylight rule' (gap between attacker and defender) was never a real law — it's just a TV term for clearly offside positions.