One evening last week, a restaurant owner in Washington Heights and two customers stood chatting on the sidewalk about the changes in the area over the last 25 years. The restaurateur, Peter Walsh, was telling the people, who were coming from a hospital on 168th Street, how much safer the neighborhood had become as he stood in front of his restaurant, Coogan’s, on Broadway between 168th and 169th Streets.

A surveillance video shows what happened next.

A stocky man in a white T-shirt strode across the sidewalk, directly to where Mr. Walsh and the two people were speaking. In an interview Wednesday, Mr. Walsh provided the soundtrack:

“Give me some money,” the man demanded.

“Excuse me?” Mr. Walsh said. “That’s not manners.”

Mr. Walsh stepped between the man and the two patrons. The man then made a threat using vile language, Mr. Walsh said, so he replied with a joke, hoping to bring the temperature down. It did not work.

The man shoved Mr. Walsh hard, knocking him back a step.

A 68-year-old restaurant owner was about to begin slugging it out with a 53-year-old man who was living around the corner in a shelter that holds 200 mentally ill homeless people.