8:20 PM PT -- TMZ has obtained new video and info that sheds more light onto the Killer Mike situation -- including the fact that he's now being booked for battery on a citizen's arrest ... this after he allegedly got physical with a security guard at the venue, while out in the rain.

Law enforcement sources tell TMZ ... Mike was booked for misdemeanor battery Sunday evening, this after a private person's arrest took place at Crypto.com Arena. We're told KM is accused of knocking down a security officer after they did not get out of his way quick enough -- the apparent aftermath of which looks to have been caught on tape, seen here.

We got a hold of video that seems to show Mike being chased down outside in the windy rain, where security personnel can be seen attempting to stop him ... with Mike looking determined to get by them. You can't see any "knock-down" as has been described to us by law enforcement -- but it does look like he faces off with security guards in tense fashion.

Eventually, Mike was cuffed and led away in the rain as well. It's still unclear what exactly led up to this -- remember, just moments earlier, he was inside soaking in the Grammy win.

Killer Mike's Grammys night came to an early end ... because he was just led out of the event in handcuffs -- after an alleged physical altercation.

A journalist for The Hollywood Reporter posted video to X showing the Run The Jewels rapper leaving the venue with a police escort ... hands bound behind his back.

The 48-year-old doesn't look particularly concerned as he's being led away ... chatting amicably with a man who is walking alongside him and police before saying hello to someone else in a tuxedo.

Law enforcement sources tell TMZ ... Killer Mike was detained after allegedly getting into some kind of physical altercation with a security guard at the event.

We're told he's not under arrest, and officers are still trying to sort out exactly what happened.

It must feel like an emotional roller coaster for KM and his fans after an afternoon full of highs.

Mike's already got his Grammys ... he took wins in all three categories he was nominated for including Best Rap Performance, Best Rap Album and Best Rap Song -- though his win in the last contributed to some controversy and conspiracies.

We've reached out to Killer Mike's team ... so far no word back.