Actually, even though I agree on many points of view expressed by you and JCboy, that isn't the reaction I had. I thought it was pretty appropriate that she slapped the boy considering he was participating in a riot. After all, The mother saw her son on television throwing rocks at police.
I'm loathe to agree with these other two on anything, FWIW.
I agree - granted I do not normally support smacking your child in the head in public, but this boys actions were very extreme and could get him in huge trouble. I do not like the swearing and hitting, but certainly understand her reaction. She flew off the handle understandably - and maybe did something extreme but it was much better than the other parents that did nothing.
Her child must know his behaviour is not tolerated. I know some people are saying if she didn't do this or that then he would not have been there in the first place --- I do not necessarily agree. When she called him out and smacked him - he didn't fight her - he knew she wasn't taking his crap.
Maybe not the ideal handling, but it seemed effective and she certainly got her point across so why would I argue with her tactic.