I put paint splotches on two sheets of newspaper and he painted the splotches all around. Then I cut triangles out of the sheets of painted newspaper.
He glued the squares to a box I had sitting around the house (an obscene amount of boxes come and go due to work materials that my office mails here). He loves using glue sticks and sticking paper to the glue. We've only used glue a few times but it's one of his favorite crafty things to do.
I cut a triangle in the box and now he can throw balls through the triangle. I put a laundry basket behind the box to keep it stable (as opposed to putting something heavy in the bottom) and the laundry basket catches just about every ball he throws through; bonus! We are grouchy today but this activity was a ton of fun and we'll be able to play the new game for a long time. I think he might know what a triangle is by the end of the day. We've only said it a billion times already this morning. Every time he's about the throw the ball through the hole I say "see if you can throw the ball through the triangle."
Since I only used items that we had around the house for this craft, our crafting time and our new activity were completely FREE! One of my favorite things about being frugal is finding things to do with stuff that's already lying around.