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