noun
foot fault
Tennis term: a fault called when the server's foot touches or crosses the baseline or sideline before the ball is struck.
サーブのときにフットフォールトを取られた。
I was called for a foot fault on my serve.
Variant with a middle dot; less common but still seen.
A general fault in tennis; フットフォールト is a specific type of fault related to foot placement during the serve.
Borrowed from English 'foot fault'.