The confrontation happened during a timeout early in the second half of Cal's 76-68 win over Southern California on Sunday night when Montgomery yelled at star guard Allen Crabbe for nonchalant play and then shoved him in the chest with both hands.
Montgomery downplayed the run-in immediately after the game but later issued an apology through the school. On Monday, he acknowledged he went too far trying to get his star player out of a funk.
"I made a mistake," he said in an interview with Pac-12 Networks. "There's no question about that. Allen is so important to us. There's a lot of pressure on Allen. He's got to perform for us. People are holding him, they're pushing for him, they're physical with him. It's very difficult for him. He, like everybody else, I'm sure he gets tired of that.
"Sometimes he tends to take himself out a little bit. Yet for us, he's our leader. We can't play if Allen is not engaged. To his credit, he generally has been but in this particular game I thought he was a little bit out of it."
Crabbe had to be forcibly restrained by teammates and briefly left the court before coming back and leading a comeback victory for the Golden Bears (16-9, 8-5 Pac-12).
Athletic Director Sandy Barbour said in a statement late Sunday night that she understood the game was emotional but Montgomery's actions were inappropriate.
"It is unacceptable for our coaches to have physical contact with student-athletes regardless of the circumstances," she said. "The second-half incident was certainly out of character for Mike Montgomery, and I am confident that something like this will not happen again."
Montgomery tried to make light of the controversy in the postgame news conference, smiling and saying the move motivated Crabbe. He also said he would do it again.
"Worked, didn't it?" Montgomery said of the exchange with Crabbe. "Allen had come down twice went to the wrong side of the court and his guy shot two 3s. I was trying to get him going. Probably overdid it a little bit but Allen's my guy. We can't win if he is not ready to play."
Crabbe, the leading scorer in the Pac-12 with an average of 19.8 points, scored 14 points after the shove and led the Bears back from a 15-point deficit to win.
Montgomery later apologized in a statement released by the school.
"I have great passion for this game and tonight, I let my emotions get away from me in the heat of the moment," Montgomery said. "While my intent was to motivate our student-athletes, my behavior was inappropriate and I apologize for my actions."
Crabbe said after the game that emotions were high at the time and Montgomery was just trying to motivate him.
"Everything's fine," Crabbe said. "It's under the bridge. He's my coach, no hard feelings. We're just going to keep moving on."
On Monday, State Sen. Leland Yee called for Montgomery to be suspended.
“While I have a lot of respect for Coach Montgomery and I appreciate his apology, his actions at last night’s game are completely unacceptable," Yee said in a statement. "As a psychologist, I can assure the university and Coach Montgomery that physically pushing a student-athlete does nothing to motivate them. We do not accept such behavior by our professors and administrators, and we should not tolerate it with our coaches.
"The game was an emotional one, but representatives of UC – especially adults – need to be able to control their emotions and refrain from physical altercations with students. I urge the university to take swift disciplinary action of at least a one-game suspension and I wish the Cal basketball program the very best as they enter the final games of the season."