The kid cut the cop. Adult, teenager or child, cutting a policeman with a knife is a great way to get yourself shot.

Apparently the wounded officer did not have a taser which is unfortunate since this was a textbook case for its use. However, it still stands that attacking someone with a knife is lethal force and can be answered as such.

Armchair quarterbacking is all fine and good, but without actually being there you can't really pass judgement.