Twenty One Pilots Singer Tyler Joseph Slips on Drumstick, Falls Onstage

Twenty One Pilots frontman Tyler Joseph took a nasty fall in the middle of the band's show ... messing his leg up pretty bad thanks to a rogue drumstick.

The band took the stage in Cleveland, OH Tuesday night ... the crowd was as hyped as Tyler and co. were throughout the night, especially when the singer jumped off a high platform to run across the stage -- big mistake.

You can see Tyler slip and crash onto an elevated part of the stage ... while he seemed to recover quickly, things looked worse for wear after the show ended.

The band posted an explanation backstage, with drummer Josh Dun saying he dropped one of his sticks on stage -- something he rarely does.

He says it was unfortunately Tyler who found the stick with his foot, twisting his ankle in the process and slicing his knee open.

Josh felt pretty bad about leaving his stick out there, but don't fret, Tyler -- dinner's on him!!!