Insane Video Surfaces from '12 Casino Brawl

NY Giants linebacker Jonathan Casillas should've been a running back -- because it took 5 SECURITY OFFICERS to bring him down during a violent casino clash back in 2012.

We've been making calls for days trying to gather all the info about this crazy video -- and though the details are scarce, here's what we know ...

-- It happened at 6 AM on May 12, 2012 at the Harrah's Casino in Atlantic City

-- Before the video begins, Casillas was pissed ... and walked outside to cool off. You see him throw a potted plant across the valet area.

-- Casillas went back inside and was confronted by several security officers. Things get testy, Casillas tucks his chain, a security officer shoves Casillas and…