Tony Hawk says a failed attempt at a popular skateboarding move led to his severely broken leg on Monday ... and now, the skate legend says he's hoping to one day be able to walk again "unaided."
The 53-year-old finally went into detail on Thursday about what caused his broken femur earlier this week ... and he says an effort to do a McTwist (a front flip with a 540-degree rotation) in the half pipe busted up the limb.
Hawk explained he had "very little speed and an unsteady grab" while trying the trick -- and when he came crashing down on the ramp, his leg crumpled.