In a move with little precedent in professional sports, the N.B.A. is putting the weight of its multibillion-dollar brand and the prestige of its star athletes behind a series of television commercials calling for an end to gun violence.

The first ads, timed to reach millions of basketball fans during a series of marquee games on Christmas Day, focus on shooting victims and contain no policy recommendations. The words “gun control” are never mentioned.

But the organization that paid for them, Everytown for Gun Safety, has a robust and controversial agenda: It was founded by former New York City Mayor Michael R. Bloomberg specifically as a counterweight to the National Rifle Association, and the group also battles at the local, state and federal level to expand background checks for gun buyers, strengthen penalties for gun trafficking and ban gun sales to people convicted of domestic abuse.

The N.B.A.’s involvement suggests that a bloody year of gun deaths — in highly publicized mass shootings and countless smaller-scale incidents — may be spurring even some generally risk-averse, mainstream institutions to action.