Size does matter in that case. That's why clubs hire big guys.
Yah really need the mass to be able to grab him and hold him if it comes to that.
Then again I once saw a little guy that could not have weighed more than 100lbs soaking wet drop two huge bouncers at a bar on the LES. Sloppy drunk, too. He obviously had had some martial arts training. Moved real fast, even drunk. Fist one put his hand on the kids shoulder to eject him, and the kid spun around like a whirlwind and the bouncer went down with an elbow to the side of his neck. Didn't quite see what he did to the second, since everyone was standing on their stools by that time to gawk at this kid in action. Found out after the fact this kid was supposedly known in the neighborhood for doing strongarm assault/robberies.
But in any case, that sure as hell ain't me. I can count the fights I have been in in my adult life on one hand with fingers left over Three and Oh might be a good record, but it's not a very experienced record.
If I did wind up working any security i'd simply have to get my ass a carry permit. (since it would not be in NYC, and I could get one if needed)