A man with a semiautomatic rifle opened fire at a church festival Saturday, wounding his ex-wife and two bystanders before festival-goers grabbed him and held him for police, authorities and a church official said. Witnesses described a chaotic scene, with people screaming and running for the exit after gunfire rang out on a grassy field where the festival was being set up at the St. John Baptist de la Salle Roman Catholic parish in Granada Hills, a suburb of Los Angeles. "I heard bang, bang, bang, bang. It sounded like balloons popping," said Jeff Sempelsz, a church volunteer who was setting up a booth when the man started shooting. "I didn't know what it was but I could see the rifle in his hand." Father Robert Milbauer, the parish's pastor, said a woman injured in the attack was the gunman's ex-wife. The two have a child who attends the school and had been mired in an ongoing dispute, Ruiz said. "We believe this is an isolated incident, a domestic-violence dispute," police Capt. Steven Ruiz said.