An illegal play in football in which a player swings his leg horizontally in an attempt to make contact with an opposing player's leg. The leg whip was banned due to the likelihood of injury occurring because of the awkward contact with the leg. It is considered an unsportsmanlike conduct infraction and is penalized 15 yards. In extreme cases where intent to injure is possible, the offending player may be ejected.
The leg whip was banned quite some time ago due to concern over leg and knee injuries. The angle of contact from a leg whip can put a great deal of strain on an opposing player's knee and could cause significant damage. A bad knee injury could be a career ender for a player, so the tactic was made illegal. It is rarely seen in modern day football as it almost automatically brings a penalty on the offending team.