Foot Fault

The rules require the server to stay behind the baseline and within the imaginary extensions of the center mark and sideline until after the ball is struck. Common foot faults include stepping on or over the baseline before contact, sliding a foot forward during the service motion so it crosses the line early, or landing on the wrong side of the center mark extension. A foot fault results in the loss of that serve attempt exactly like a serve landing outside the box — a foot fault on a first serve simply moves to a second serve, while a foot fault on a second serve is a double fault and loses the point.

Foot faults are called by officials at professional and many competitive amateur events, but in casual and most recreational self-officiated matches they typically go unenforced unless clearly egregious, since players are not standing where they can accurately judge their opponent's foot position relative to the baseline. Players developing an aggressive, forward-driving serve motion sometimes develop a foot-fault habit without realizing it, since the forward momentum encourages the front foot to creep across the line early — video review is one of the few reliable ways to actually confirm whether a foot fault is happening.