From the ARL's laws of the game....
"KNOCK-ON means to knock the ball towards the opponents’ dead ball line with hand or arm, while playing at the ball."
"REBOUND is an ACCIDENTAL STRIKE: when a ball strikes a player who makes no attempt to play at the ball."
"A player shall be penalised if he deliberately knocks on."
"If, after knocking-on accidentally, the player knocking-on regains or kicks the ball before it touches the ground, then play shall be allowed to proceed."
So, how is it that we regularly see defending players go unpenalised for deliberately knocking the ball forward to stop a pass, or tapping it forward in an attempt to control the ball and intercepting it?
If the first action is to deliberately knock the ball forward, it should be a penalty. I haven't seen this penalty enforced since the early 1990s.