But the security guard's tackle, while effective against an opponent not expecting it, wasn't good form-wise.

Cops don't charge people. Cops just arrest 'em - prosecuting attorney's issue the charges.

If someone dressed as an officer during Halloween committed a crime and his impersonation aided in that crime, then they would be arrested...just as this guy was. The fact that he came in dressed in attire similar to an official, ran into the field blowing his whistle, and came in with the stop clock signal, all in a manner to impersonate the game official, I feel no sympathy for the accused here. And in reality, this will probably end up being pleaded down.