Most forms of football have a move known as a tackle. The primary purposes of tackling are to dispossess an opponent of the ball, to stop the player from gaining ground towards goal or to stop them from carrying out what they intend.

The word is used in some contact variations of football to describe the act of physically holding or wrestling a player to the ground. In others, it simply describes one or more methods of contesting for possession of the ball. It can therefore be used as both a defensive or attacking move.

In Middle Dutch, the verb tacken meant to grab or to handle. By the 14th century, this had come to be used for the equipment used for fishing, referring to the rod and reel, etc., and also for that used in sailing, referring to rigging, equipment, or gear used on ships. By the 18th century, a similar use was applied to harnesses or equipment used with horses. Modern use in football comes from the earlier sport of rugby, where the word was used in the 19th century.

Unlike other codes, tackles in association football have to be predominantly directed against the ball rather than the player in possession of it. This is achieved by using either leg to wrest possession from the opponent, or sliding in on the grass to knock the ball away. A defender is permitted to use their body to obstruct the motion of a player with the ball, and this may be part of a successful tackle. Pulling a player to the ground in the style of tackle common to other codes is completely absent from the game (this would be considered "violent conduct" and result in a red card (dismissal)).

Although some contact between players is allowed, the rules of association football significantly limit the physicality of tackles, explicitly forbidding contacts which are "careless, reckless or [use] excessive force". Almost all tackles where the tackler's legs make contact with the opponent before the ball are considered illegal, and heavy contact after initially touching the ball may also be penalised.

Illegal tackles are fouls and are punished with a direct free kick (or penalty if committed within the penalty area) for the opponent's team. Such incidents are common, with dozens of occurrences in a typical match. In most cases these fouls are not considered misconducts, however yellow cards (cautions) may be delivered for more egregious fouls that constitute "unsporting behaviour". If a foul tackle endangers the tackled player's safety, it is likely to be considered as "serious foul play" by the referee and punished with a red card (dismissal).

Tackles that involve lunging at an opponent with both legs, regardless of whether the ball is won, are generally considered to constitute serious foul play and hence result in a sending-off.^{[citation needed]} This explicitly includes "scissoring"^{[citation needed]} (tackling with legs apart, so as to trap the opponent's leg or legs in between), which is likely to be punished with a sending-off (red card), as it poses a high risk of severe knee injury to the player being tackled. Tackling with studs up is considered dangerous. A studs up tackle is made when a player lunges into a tackle with a leg or both legs outstretched exposing the soles of their boots. Referees are encouraged to at the very least caution (yellow card) players who commit such challenges.

Additionally, an illegal tackle which is also a professional foul is considered misconduct.