NEWPORT BEACH, Calif.—A 21-year-old San Diego former Marine reached a plea deal agreement with prosecutors on July 14 in connection with a St. Patrick’s Day fight that killed a man in a Dana Point restaurant.

Jack Griffin Isaacson—who was facing a felony count of involuntary manslaughter—pleaded guilty to a felony count of battery with serious bodily injury. He was scheduled to be sentenced on July 12 of next year.

Sentencing was postponed for legal technical reasons to allow for the felony count reduced to a misdemeanor, his attorney John Barnett said. Mr. Isaacson will begin serving a six-month term of home confinement on Aug. 10.

Mr. Isaacson, who had been stationed at Camp Pendleton at the time, punched 38-year-old Michael Terry of Laguna Niguel, who was rushed to an area hospital where he was pronounced dead the next day, according to the Orange County Sheriff’s Department.

Deputies were dispatched to Beach Harbor Pizza at 34473 Golden Lantern about 7 p.m. on St. Patrick’s Day last year when the two men got into a fight, sheriff’s officials said. Barnett said Terry was drunk and was acting aggressively toward customers when he got into a conflict with Isaacson, who is a boxer, Barnett said.

“He’s remorseful a death resulted from this,” Barnett said.