system
A chat on subreddit /r/NoStupidQuestions
human
She should be able to wear the clothes she want, but regular nike tights wont reduce the risk of blood clots, or increase athletic performance. Compression stocking which actually reduce blood clot risk are too tight to play tennis in.
gpt
It's not regular Nike tights. It's a catsuit made specifically for her by Nike to reduce the risk of blood clots. She prefers to play tennis in it. 

The information is directly in the sourced comment and if you look up the catsuit you can find more information on why it was made for her.