Foul基础含义是指令人生厌的恶臭，或者令人不愉快的，犯规的。所以就容易理解Fall foul

of是指冒犯某人或与某人起冲突的意思了。

Jack Ma已经惹恼了当局。 Jack Ma, has fallen foul of the authorities    

如果我们不向税务官员报告这件事，我们就是违法的。If we do not report this to the tax officer, we will fall foul of the law.

尽量不要得罪我们的老板，因为他会很令人不愉快的。Try not to fall foul of our boss, as he can be very unpleasant.