In gridiron football, an onside kick is a kickoff deliberately kicked short in an attempt by the kicking team to regain possession of the ball. This is in contrast with a typical kickoff, in which the kicking team kicks the ball far downfield in order to maximize the distance the receiving team has to advance the ball in order to score. The risk to the team attempting an onside kick is that if it is unsuccessful the receiving team gets the ball and usually has a much better field position than with a normal kickoff.

The onside kick has a low success rate, though its chances of success increase in a situation where the returning team does not expect it. It is generally only seen late in a game when a team has just scored but is still trailing by 8 points or fewer (the most points that can be scored on a single possession) and needs to regain possession in order to score again before time expires.