top coat for spray painted basketball backboard?

I made a simple basketball backboard for my kids out of some maple plywood.
I spray painted it white and red and now I want to put some sort of protective top coat on it as it will be outdoors and take a lot of abuse and moisture.
I'm planning on giving the paint a couple days to cure.

Polyurethane a good choice here? I'm thinking at least semi-gloss, if not gloss.

tia
Attachment 419776Attachment 419777

Polyurethane has a slight yellow cast to it when you apply it and continues to yellow as it ages. This would look bad on the white. You would probably be better off using some rattle can clear however be sure to read the instructions on the red and white paint. There is probably a recoat window. It means where it says put all the coats on within an hour or so or wait something like 72 hours. Since you don't know if the paint is completely compatible I would let the paint dry a week before topcoating. What happens when you rush a recoat window is the solvents in the clear coat are so strong it causes the base coat to lift like you put paint stripper on it. It wrinkles and bubbles up.

You need an exterior rated product. Due to the abrasiveness of the task that a backboard experiences, expect to have to clean it up periodically since most finishes available to the "ordinary consumer" are not going to have the same level durability of some of the more industrial products available for manufacturers. (But even those wear)

thanks jim.
my big box store has an exterior grade spar urethane (Varathane brand) that is oil based. is that a good place to start?

A clear coat brings risk and you may not be able to repaint it. Just plan to repaint it occasionally. Are you on the rainy side of the island?