First, just because the guard was walking away with the sign, does not mean he took the sign from him, or for no reason.
Let’s wait and see what the facts are before we decide things. We wouldn’t want to be Judge and Jury, on FR, would we?
Most of the posters here have already convicted the guy who was punched. Judging just from the video, it appears that the guy was trying to recover stolen property when he was assaulted by a strong armed robber.
How are you going to decide the "facts"? By just assuming that the guy was assaulting the guard for no reason at all?