butttumbled 

when you slip down the stairs and hit your ass on every step down.

man i was so messed up last night i slipped runnin down my steps and butttumbled all the way down em yo. wurd.

butttumbled by Kartwheel February 16, 2009

Buttfumble 

(Noun-Verb) - To run directly into your offensive lineman's rear end so violently that it in turn causes the quarterback to misplace the pigskin out of his hands and onto the ground ultimately causing a fumble.

Mark Sanchez is the pioneer of the Buttfumble.

Buttfumble by KRHimself December 30, 2012