Undercut

Sometimes it can be difficult to know the difference between a player jumping at an opponent and a player being undercut. 

One of the ways to tell the difference includes observing who initiates contact. If it is a jumping-at offence, the player in the air is moving toward the opponent. If it is an undercut, you will notice that the player who is on the bottom moving their body to the opponent.

In this video below, you will see a defender slighly moves his body to the lower half of the attacker's body. The force is relatively small. But when a body is in the air, it does not take much force for it to lose balance. This is an example of an undercut offence.