I'm not 100% sure myself how score is kept, but I did do a quick google search on it, and it seems that it's kinda like tennis with walls... one person serves it and it can only bounce on the ground once before the other person has to hit it back. If the receiver misses it or gets hit, the server gets a point. If the server messes up the other person doesn't get a point, but does get to serve..
Or something like that
