12:30 PM PT -- Sources connected to the investigation tell TMZ Sports ... when cops responded to the club for a possible shooting, they ordered everyone to get down and not move so they could properly search and investigate.

We're told Bennett did not stay put -- instead, he ran -- and a cop outside the club stopped him and ordered him down to the ground at gunpoint.

Our sources say Bennett was detained until cops could determine he was not involved in any possible criminal activity ... and he was released.

TMZ Sports has obtained video of NFL superstar Michael Bennett being handcuffed by police while lying face down on the concrete in Las Vegas ... and you can hear him screaming that he's innocent.

The video was shot outside Drai's Nightclub on August 26 -- you can see one officer take position on a balcony while another cop handcuffs Bennett on the street level.

During the incident Bennett screams out, "I wasn't doing nothing man! I was here with my friends! They told us to get out, everybody ran!"

Bennett claims the officer had pulled a gun on him and threatened to "blow my f*cking head off" -- but you don't see that in our footage. At the time the video begins, Bennett is already being cuffed.

WITNESS ACCOUNT
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You can see the officer on the balcony is clutching something in his hand that resembles a handgun -- but it's unclear. 

Bennett has said in a statement that he -- and several hundred other people -- were running from the club after hearing what they thought were gunshots. He claims cops stopped him for "being a black man in the wrong place at the wrong time."

We've reached out to the Las Vegas Metro PD for comment -- we're told they're investigating the incident.