A source close to Conor tells us the fighter wanted to say hello to MGK, stuck his hand out and started walking up to the singer. We're told MGK said something -- that Conor couldn't hear -- and MGK's security pushed Conor away. Our source says Conor doesn't understand what the issue was, and was surprised by how he was treated.
Sources connected to the situation tell us Conor asked MGK for a photo, which Kelly denied ... and that apparently escalated into him pushing Conor, whom we're told stumbled back and spilled his drink.
When he collected himself and whatever was left of his drink, our sources say Conor allegedly chucked the drink at Kelly ... as well as Megan, whom we're told was nearby.