Reply to what is the deal with the derailing backspin?

i feel dumb for asking...

so in some radio shows and basically every boiler room set i've seen - there will be a couple of times during the set when someone in the crowd or the mc, or even the dj, reaches over to the decks and does a backspin on the active deck which derails the set, then the music stops. and everyone seems pretty happy about it?

then they play that same song again from the start. and the dj set continues.

http://youtu.be/Tmf44ZIYCKo?t=22m20s - dj does it @ 22m20
http://youtu.be/Tmf44ZIYCKo?t=25m55s - random guy in crowd does it like 3 mins later
http://youtu.be/Tmf44ZIYCKo?t=31m20s - mc does it 5 mins after that


is it like a tradition or a dancehall thing or something? what does it mean o_O

it never happens in the clubs i've been to

please pardon my ignorance :P