There are better options. 
The underlying ethos in the AFL rules is that almost anything is permitted so long as you are going for the ball. If you clobber someone because that’s what you need to do to get to the ball, fine. If you clobber someone just for the sake of clobbering them, or deliberately use more force than necessary, not so fine.
Because it involves big strong dudes running around at speed, collisions happen. The rules are designed to minimise contact with the head [1], but sometimes accidents occur and somebody gets concussed.
But that is a thing that might happen to a player a few times in their career. They are not slamming their heads together at every scrimmage.
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[1] To tackle someone, you have to grab them between shoulders and hips; no tripping, no coathangers, no charging into their back. If you run into someone, you aren’t allowed to deliberately or negligently hit them in the head.
