Who else wanted to smack the kid?

I would have if he was putting his life and my life in danger.

I certainly did.

Boycott movies that involve real animal violence! (and their directors too)

The thing I don't get about kids like that: if he freaks out about being touched, what if you grab him and don't that go? Hold him and he will spaz out for a while but eventually run out of energy and maybe then get over the "no touch" rule? I don't understand autistics very well. Just know with normal kids if they throw a tantrum over something stupid you can leave them be until they realize they have to deal with it.

What would be the right thing to do in a mortal danger situation?

A special needs child is being physically uncooperative, even violently opposing your attempts to keep them safe or get them to safety.

You don't have time to go through whatever routine(s) that is/are used under normal circumstances to get them to comply.

So what do you do?