Made dirty or caused something to become tangled or blocked; in sports, committed an unfair act against an opponent.
From Old English 'ful' meaning 'dirty' or 'foul.' Originally referred to physical uncleanliness, then expanded to mean morally wrong or in violation of rules.
A basketball player who fouls out has committed five personal fouls—the rule exists because early basketball had so much physical contact that games became dangerous brawls!
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