Tumbersault
A running dive into a summersault, or forward roll. May also be completed rolling sideways on ones back.
The boy was seen doing a tumbersault in the middle of the road to escape the police.
tumbersaulting
A confusing and dizzying combination of tumbling and somersaulting while one is in mid air, usually a result of a botched high dive.
"Those guys look ridiculous, tumbersaulting through the air like that"