My guess is that the assumption is a player 'leaving the ground' is aiming for the head as they are looking for a higher hit. Or that's whats behind the AFL's thinking.This has always bothered me
Not jumping makes the bumps far more severe
It means that you are braced against the ground so can hit harder. Plus not jumping leaves your head in the impact zone so you get KOs like Kelly yesterday.
If you want to do some damage, stay grounded.
If you want to do a spectacular, showy hit where you bounce off each other but do less damage - jump in the air.
Yet somehow jumping in the air is seen as being worse in terms of intent.
Roo didn't jump when he collected Kemp.