For the shorts I used a pattern that I found on SewAdollable.com: Easy Shorts Pattern. The shorts were a little small, so I am not going to use this pattern again without altering it.
The top was a free pattern on LibertyJanePatterns.com: Free Pattern for American Girl Doll T-Shirt. To make it a tank, I just left out the sleeves. I folded over the armholes and hemmed them.
I used an old basketball jersey I had as material. The jersey was reversible, so the inside of the doll outfit is white, and the outside is red.
I chose not to put anything on the front or back, such as a team name or player number. It’s more of a practice uniform for my doll, rather than a game outfit.