A foot fault is when a tennis player steps on or over the back line of the court while serving. When an umpire calls this, podiatry is consulted to evaluate the tennis player's foot and, if needed, amputate.
Conversation Between Podiatrist and Roger Federer
FEDERER (to the podiatrist): Is it bad?
PODIATRIST: I'm afraid not, sir. We're going to have chop off these legendary feet of yours.
PODIATRIST: Sorry. It's not one foot at fault here; it's both.
FEDERER: But how will I keep playing?
PODIATRIST: You're Roger Federer. You can do anything. I believe in you.
FEDERER: I am Roger Federer. I can do anything. You're right. Okay, take them off!