SXSW Bully sucker punch. Justified or cheap?

Alexander said

If he deserved it it doesn't matter if it's cheap.

But everyone swarming around to take pictures of the guy on the ground with their phones was hilarious and frightening at the same time.

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This. He deserved it (he was obviously trying to pick a fight with unwilling participants, knocking him out was a service to public safety) but the crowd reaction was more disturbing and notable in my opinion.