Hundreds of boxing fans were whipped into a frenzy after the Floyd Mayweather fight Saturday night ... and things got so out of hand one guy ended up in the hospital.
Moments after Money scored a unanimous decision over Marcos Maidana ... 2 fights broke in in the lobby -- causing scores of fans to run back inside the arena to avoid the fight.
One man was taken away on a stretcher ... but hotel officials tell the Las Vegas Sun -- he wasn't fighting ... he just got stampeded.
In case you forgot ... a similar incident went down after the Mayweather fight in May -- only that one was worse ... 24 people were hospitalized.
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