Nick Young Goes BALLISTIC ... Police Chopper Dispatched (VIDEO)

Nick Young had a complete MELTDOWN outside of Dave & Buster's in L.A. Saturday night ... after his entourage got into an altercation inside the bar ... TMZ Sports has learned.

It's unclear what triggered the fight, but it sent Swaggy into a RAGE. The video shows Young ripping into his buddy, accusing him of instigating the drama ... then chucking a water bottle in his direction.

LAPD showed up, but the angry group was so large officers needed backup, including an LAPD chopper.

Cops asked the group to leave and everyone cooperated. No one was arrested.

Check out the video -- it's crazy.