Marlon Gayle says his brother Bobby was preparing to do some work with a friend when a driver almost hit them.
When Bobby threw up his hands and signaled for the driver to slow down, the situation escalated.
Gayle said the man parked his truck, got out, said a racial slur, and then he started shooting.
"It's a heightened level right now. We take these types of crimes very seriously, and so we're investigating it to the fullest," said Stockton Assistant Police Chief Jim Chraska.
Bobby was shot seven times but is expected to be OK, Gayle said.
Surveillance footage documented the violent encounter. Investigators are now using the video to try to identify the suspect.
Anyone with information is asked to call the Stockton Police Department.