cause if i knew them fairly well (like, we've conversed from time to time at a minimum) then i would probably either call (if i had the number) or knock and ask something like "hey, is everything ok over there? you guys are making a lot of noise and i'm trying to sleep"

if i don't know them at all, and they're to the point where the building is shaking because of *something* being thrown around, then i might consider calling the police. i guess i'd have to hear how bad things seem to be before making that call...