Not trying to steal anyone's thunder here, but I was so taken with this little program when I saw it earlier today on Twitter that I thought it might be fun to make it somewhat interactive, so that the players could actually influence the path of the balls using the keyboard, and also activate a "speedup" (mode but at the expense of their ability to influence the path). I also added some charts to track the state over time. You can "play" it here:

https://dicklesworthstone.github.io/ball_fighters/

And code is here:

https://github.com/Dicklesworthstone/ball_fighters

I give full credit to the original author of this post FWIW.