Lakers' Lou Williams Cuffed In Vegas ... 'I Did Nothing Wrong'

TMZ Sports has obtained footage of Lakers guard Lou Williams handcuffed by police and slammed up against a cop car in front of a casino in Vegas ... but the NBA player insists he did NOTHING wrong.

We've learned ... Williams was detained in front of The Cromwell hotel and casino on the Vegas strip in the early hours of September 13th ... after the Mayweather vs. Berto fight.

Witnesses at the scene tell us, Williams was involved in an altercation with "a large man" -- and cops rushed in to break it up. We're told Williams adamantly denies being involved in a fight.

Williams was handcuffed and slammed up against a police car -- but the Las Vegas Metro Police Department tell us they have NO RECORD showing Williams was formally arrested that night.

We spoke with Lou's agent Wallace Prather III who tells us, "Apparently there was an issue that [Lou] wasn't involved in, which is why they didn't arrest him."

"If Lou was fighting in public in Las Vegas they would have arrested his ass ... he wasn't fighting anyone."

Eventually, cops released the cuffs and Williams was sent on his way.