Prosecutor Lisa Luzaich told Justice of the Peace Melissa Saragosa that Mayweather has been in trouble before and hasn't been punished.
"He just continually gets himself into trouble, and he is able to get himself out of it as well," she said. "Essentially it is because he is who he is and is able to get away with everything."
"The only thing that's going to get this man's attention is incarceration," the prosecutor said.
Mayweather stood still in a striped olive vest and showed no reaction when the judge imposed the sentence and told him he must report to the Clark County jail on Jan. 6.
Mayweather's lawyer, Karen Winckler, said she may appeal what she called an unusual sentence.
Mayweather would likely serve most of the 90-day sentence, but he could serve several weeks less if he gets credit for good behavior, said Officer Bill Cassell, a Las Vegas police spokesman.
Mayweather and his manager, Leonard Ellerbe, declined comment outside the courtroom.
The judge said she was swayed by Mayweather's admission that he hit Josie Harris and twisted her arm, and that two of their children, ages 9 and 10, witnessed the attack.