Investigators said the deputy was following the suspect on the 10 Freeway at about 4:30 a.m. Wednesday when the man caused the deputy to veer toward a freeway side rail. That's when the deputy fired his weapon and hit the suspect once in the forearm.
The two exited the freeway at Mateo Street, and authorities arrested the suspect at 41st and Alameda streets.
The suspect, whose identity was not released, was transported to USC Medical Center where he was listed in stable condition.
The off-duty deputy was not injured in the incident.
Deputies said the suspect committed an assault with a deadly weapon involving his car. It was unknown if the suspect's car actually hit the sheriff's deputy's car or if the man was just driving toward the deputy quickly and the deputy felt threatened.
The close encounter with the two vehicles prompted the deputy to shoot at the suspect.
No further details about the incident were available.
Witnesses said they heard gunshots and cars speeding away. Skid marks were seen on the road.
The incident was under investigation.