Charles Miller, 42, was caught on camera during a mass honoring baseball legend Roberto Clemente at Newark's Cathedral Basilica of Sacred Heart on Saturday, police said.
In the video, Miller can be seen strolling up the altar and slugging Rev. Manuel A. Cruz, the auxiliary bishop of the Archdiocese of Newark, officials said.
Police quickly tackled Miller and took him into custody.
Cruz was reportedly taken to the hospital for his injuries but they were not serious.
James Goodness, spokesman for the Archdiocese of Newark, was saddened by the ordeal.
"We are thankful that law enforcement officers were able to apprehend the assailant," Goodness said. "This is not something that we expect to happen in any of our churches."
The Saturday event was in honor of Clemente, the Baseball Hall of Famer, who died in a 1972 plane crash as he traveled to Nicaragua to personally deliver humanitarian help to earthquake victims.