[SWF=http://www.antiup.net/file/g8hthg6spw_ball_kill.swf]width=300 height=200[/SWF]

The physics are quite shoddy. All of your motions are. You have to have smoothing and easing from an inconsistent motion in up and down, going slower or faster as it goes along.

There is resizing

The motions are stiff, and they lack power.

Sorry.

Reinact the motions you are trying to make in real life, study them well and copy them in flash with stickfigures. it should be alot better. if you punch like that, you're not really human. first he needs to throw up the ball wich is affected by gravity. then he needs to "load up" the punch. and finally throw it at the ball, wich on impact increases it's speed.
also his arm kinda looks like it's dissapearing.
just try again. practise makes perfect.

here's a little guideline for a punch. just don't copy it, study the movements he makes.