Tai chi, while a martial art, is viewed by many today as a spiritual breathing and balance exercise enjoyed by people of all ages, usually performed in slow motion in a quiet park instead of a fight ring.

Mixed martial arts, or M.M.A., is a “no-holds-barred” fighting style developed over the last century from fighting styles around the world. It began to gain popularity in the United States in the 1980s. While it is violent, it does have rules — including no biting, spitting or gouging.

The fight between Mr. Xu and Mr. Wei was brutal. As Mr. Wei circled slowly, arms outstretched in a calm tai chi defense, Mr. Xu lunged, jabbed him to the floor, then used a “ground and pound” technique to subdue him. It was all over in about 10 seconds.

Mr. Xu did not respond to a request for an interview sent to his personal Weibo account a few days after the fight on April 27. Shortly afterward, his account was taken down as the authorities rushed to try to tamp down the controversy.

A woman reached by telephone at the Battle Club in southeast Beijing, where Mr. Xu works, said he was not giving interviews. She declined to give her name.

On Wednesday morning, the door of the Battle Club, in the dingy basement of a high-rise, was locked. Photographs of Mr. Xu and other M.M.A. fighters decorated the walls of the stairwell.

An electrician lingering by a cigarette shop at the top of the stairs said he practiced wushu and had come to check out the club after hearing about the controversy. He said that Mr. Xu had been right to pose his challenge, even though it had infuriated people.