It used to happen in my office, but it was usually a friday evening thing, or in one of those awkward gaps after meetings, but before lunch, and everyone was distracted anyway.

I mean my 20 was probably an exaggeration but I can remember days where 10+ battles erupted around me. If it's 1 or maybe 2 times I don't mind and might even join in but on the days when it becomes excessive? I can't get anything done! Very frustrating.

When I worked for a game development studio a couple guys brought nerf guns and shot people at work for awhile.

It got too distracting so management put the kibosh on it after about a month, though.