For the first time in his career, Floyd Mayweather got PUT ON HIS BACK during a major sports event -- and the whole thing was caught on camera!!
The 42-year-old superstar was ballin' out at the $50k Charity Challenge celeb hoops game at UCLA on Monday night where Floyd was trying to play some defense on streetball legend Bone Collector.
... but things didn't go Floyd's way -- because BC crossed Floyd over so hard, the boxer lost his footing and went tumbling to the ground.
The crowd went crazy as Bone hit his shot -- and all Floyd could do was smile as he picked himself up.
When asked why he would even try to cover Bone Collector, Floyd told fans and teammates he simply wanted the challenge ... gotta respect that.
The event was all for a good cause -- raising money for Teen Cancer America. Huge stars like Rob Gronkowski, Snoop Dogg, Kyle Kuzma, Michael Blackson, Terrell Owens, Pacman Jones and Brian Quick were also in attendance.
By the way, Gronk looked good on the court too -- hitting shots from long distance! Not bad for a retired guy!