Hi, thanks for playing.
The stamina bar is there mostly to discourage using melee as your primary way to kill enemies. I didn't want to remove it because it's handy in a pinch, but without stamina you can just spam swings and kill everything in 2 seconds flat.
I tried to balance the stamina cost so it wouldn't interfere with you too much if you were playing the way I intend for best experience + scoring, which is to toss 1 or 2 balls at a time and try to build a combo.
I'm still working on getting numbers and balance just right, so I'll take this on board and tweak the stamina use a little bit.