To become disliked or to come in conflict with due to one's actions, often resulting in further trouble or conflict. Used in the phrase "fall (a)foul of (someone or something)." Since you're new here, be careful not to fall afoul of Bill—he'll keep you off of every case if he's mad at you. I fell foul of the committee, and now, I'm not sure how to improve my reputation.
See also: fall