You've almost certainly got it with that. Displacement is enough to give the ball initial inertia in the right direction, then the "Rayleigh jet" or "Worthington jet" boosts it. It's perfect timing combined with a near perfect cannonball.
Think of the speed a splash goes skyward. If you accelerate something with more mass, especially something aerodynamic like a mini football to the same speed, it's going to shoot up like a rocket...which is what happened here.

Corey Worthington is my hero I love that fucking kid.

Tags for this video have been changed from 'James Cameron, Pandora, Sam Worthington, navi, space, aliens, mechs, fights, film' to 'James Cameron, Pandora, Sam Worthington, navi, space, aliens, mechs, avatar' - edited by dystopianfuturetoday

>> ^brain:
Why are they speaking English?

Ah. Asked by generations of Star Trek, Stargate and Star Wars fans, not necessarily in that order.
The only SciFi that solved this to my liking is Farscape. And the Hitchhiker's Guide to the Galaxy.

A possible explanation here would be that the Na'vi are speaking their own language, and you hear English because American audiences can't handle subtitles. Then the only question is how does Sam Worthington's character speak Na'vi?

Tags for this video have been changed from 'Melbourne, glasses, australia, party, news, Corey Delaney' to 'Melbourne, glasses, australia, party, news, Corey, Worthington, Delaney' - edited by jwray