Plant left the news conference with a cut underneath his right eye.
The fight broke out after both champions had a verbal exchange during their face-off before the news conference, which was in the garden of the Beverly Hilton. Plant reportedly made a comment about Álvarez’ mother, provoking the Mexican superstar to shove Plant with two hands.
Plant then stepped forward and tried to throw a left hook at Álvarez, who managed to dodge it and then threw a left hand which connected on Plant’s face. Álvarez hit Plant’s sunglasses, which ultimately caused the cut.
After the exchange happened, both fighters’ camps ran onto the stage and separated them.
Álvarez (56-1-2, 38 KOs) will risk his WBC, WBA and WBO super middleweight titles against Plant (21-0, 12 KOs), the unbeaten IBF champion, when they meet Nov. 6 at the MGM Grand Garden Arena in Las Vegas.
The Associated Press contributed to this report.