The officer, who was not identified, was a Tulane police officer and a reserve officer for the Second City Court, New Orleans Police Inspector Shaun Ferguson said.
The officer was at a basketball game at George Washington Carver High School when a person tried to enter and started an altercation with a staff member, Ferguson said.
The officer heard the interference and tried to remove the person from the school. As they got close to the front door, the person took out his weapon and fired a shot that hit the officer in the chest.
The officer was taken to New Orleans University Medical Center, where he later died.
Police do detain someone they believe is responsible, Ferguson said, but no further information was provided about the suspect or any possible motive.