From Rugby League Wiki
Jumping while fielding a kick is a tactic that players often use to gain an advantage when contesting a high ball with an opposing player.
- RLIF (2013). "The International Laws of the Game and Notes on the Laws". Rugby League International Federation. p. 24. Archived from the original on 2013-04-07. http://www.webcitation.org/6Fi4QgHxw. Retrieved 2013-04-07. "MID-AIR TACKLE 1. (b) It is illegal to tackle an opposing player attempting to field a kick whilst the player is in mid-air. The catcher must have returned to the ground before being tackled."