A loud bang was heard around 9:30 p.m. Wednesday, with smoke visible above right-center field.
Witnesses reported seeing a man in a Giants hat in the outfield bleachers throw a large firecracker into a group of people near a concession stand.
At least five people reported injuries, including dizziness and temporary loss of hearing.
Police spokesman Gordon Shyy says 21-year-old Paolo Pavone was arrested and booked on suspicion of willfully discharging and possessing an explosive, and discharging a firework in a public place.
The Giants beat the Dodgers 2-1.