foot fault

/F UH1 T F AO0 L T/
noun
  1. 1

    In certain sports, as in tennis or long jump, a fault in which the athlete's foot is in the wrong place at the wrong time.

    โ€œIn tennis, a foot fault results when server's foot is placed outside the service area prior to the ball being hit.โ€

Source: https://en.wiktionary.org/wiki/foot%20fault