look up any word, like timebomb:
 
1.
Running into a man and dropping your things as a result. Mark Sanchez is prone to assfumbling, but an assfumble can happen on the street. Walking into a man and dropping your bag or running towards the line of scrimmage and hitting your offensive lineman in the ass, fumbilng.
Football Example: Mark Sanchez has the ball, he makes contact with his lineman, assfumble! Patriots have the ball! Patriots have the ball!

Everyday example: Man, I was walking to the store when I ran into a guy and totally assfumbled my phone.
by Jesus Christ of the LDS December 01, 2012