If you just want to burn up balls but don't want it to really affect your game then can do this. this is especially effective if you still need levels.
equip a crappy ball and go to Chelsea room. play in that room and basically just hit the ball around and let the other person win every time.
Then watch the video at the end of the match also.
Chelsea is so cheap can lose a thousand of those and only be down 500k in coins.