In one of the more personal moments of the vice-presidential debate, Gov. Tim Walz said his teenage son had witnessed a shooting at a recreation center near his high school while playing volleyball.

Mr. Walz, the Democratic vice-presidential nominee, made the statement at the debate on Tuesday while answering a question about gun violence, saying the episode affected him: “Those things don’t leave you.”

The Harris campaign said Mr. Walz was referring to a shooting in January of last year, when a 26-year-old employee of at the Jimmy Lee Recreation Center shot a teenager. The center is across the street from Central High School in St. Paul, where Mr. Walz’s son, Gus Walz, is a student and plays volleyball.

The story caught many by surprise, including Senator JD Vance of Ohio, Mr. Walz’s Republican opponent.

“Tim, first of all, I didn’t know that your 17-year-old witnessed a shooting,” Mr. Vance said. “And I’m sorry about that and I just want to say, Christ have mercy. It is — it is awful.”

The governor has mentioned the shooting in the past, including at a campaign event last month in Grand Rapids, Mich.

“My own son was in a location where someone was shot in the head,” Mr. Walz told the crowd in Grand Rapids. “Too many of us have this.”