A pro bicycle rider slapped the living hell out of a fan during a big race this weekend ... hitting the guy multiple times -- and then knocking the hat right off his head!!!
It all went down during the Giro d'Italia race in Italy on Saturday ... when a spectator who was running alongside riders tripped up and accidentally knocked into Miguel Ángel López's bike.
The Colombian cyclist was thrown from his ride ... and in response -- he went OFF on the fan!!!
Who says cyclists ud83dudeb4ud83cudffdu2642ufe0f aren't still on roids?