Why does my cat attack my ankles?

Ankle ambushes are almost always play and predatory practice, most common in young, energetic indoor cats with a lot of hunting drive and not enough outlet for it. Your moving feet look like fleeing prey. The fix is to redirect that energy, not punish it. Give her real prey-style play with a wand toy a couple of times a day to drain the drive, and keep a toy handy to toss ahead of you when she’s in stalking mode. Never use your hands or feet as toys, which teaches her they’re fair game.