I believe they practice defense in depth. First a G-string as last line of defense, then a thong, then a lace panty, then body-shape short pants of light material. After all that, you get the skirt or the sport shorts. Forget it, ball boys, no way to see or get thru. ** TP for Topaz or TennisPower **.
https://www.tennisforum.com/threads/female-tennis-players-panties-or-thong.109897