The evidence given was that Mackay’s arm was limp and outstretched for the ball when the collision occurred (factually true), and that he was only 0.04 seconds later than his opponent in getting hands on the ball (also, maybe, factually true). Generally if you are bumping you don’t leave your arm our there hanging in the breeze before a collision (it’s a good way to get it broken), you tuck it in.
Should there be a distinction between a bump and recklessly clattering into your opponent? I’d say no, but the rules and the historical guidance suggests there is a difference. Remember the phrase we always hear: if you elect to bump you have a duty of care to your opponent and will be held accountable for the injury they receive.
The AFL is moving towards an all-encompassing duty of care, outside of any election to bump. Now the guidance will be if you recklessly approach the contest you have a duty of care to your opponent and will be held accountable for the injury they receive.
It’s the right step, but as Niall points out, it’s asking a lot of the tribunal to change the interpretation on the fly. The AFL should be making this case, and I expect they will (either now, or before next season).