The first act of “Fiddler on the Roof,” one of the most popular American musicals, which is performed frequently across the country, had just ended at the Hippodrome Theater in Baltimore on Wednesday night. The Russians had staged a pogrom against the Jewish residents of a village — an organized act of ethnic persecution — storming a wedding celebration.

Connor Drew and his girlfriend had just stepped into the lobby after the house lights went up when he heard a disturbance in the upper balcony.

There was shouting. In a display that shocked audience members, a man stood up and yelled “Heil Hitler, Heil Trump” repeatedly during the intermission, according to several witnesses. It was the latest in a recent string of anti-Semitic incidents in the United States. Mr. Drew said the man was escorted out minutes later.

“Everyone was whispering and consoling everyone because a lot of people were really startled,” Mr. Drew said in an interview. A woman sitting nearby was on her phone expressing fear that there was about to be another mass shooting, he added. “I wasn’t afraid of violence. I was just more afraid of the situation in general and seeing how people were shaken by it.”