That person was taken to the hospital in unknown condition. The deputies shot him.
An argument ensued and nearby deputies responded.
Sheriff's officials could not immediately be reached by The Associated Press about the shooting.
Seconds after the horses in Del Mar's 10th and final race crossed the finish line, gunshots were fired outside the track's fountain admission gate, according to numerous reports.
Maurizio Sarri reveals why Ruben Loftus-Cheek is struggling for playing time
I didn't know him or the players, but I knew the situation. "I am happy with him and he has improved a lot in the last 10 days". He's very young for a striker, he can improve more. "Cesc is still out", he said. "He is working in water.
Within minutes there was a heavy police presence as San Diego County deputies streamed into the track and a helicopter was seen overhead.
Video posted to Twitter appears to show a man surrounded by two deputies and holding a handgun in the air.
Following the shooting, the concert moved "forward as planned", the racetrack said. The man then falls to the ground.
Deputies returned fire, according to the sheriff's office, and the man was struck.
Twarit Vishwa: Four killed in bus crash in New Mexico
Preliminary information indicates a semi-truck traveling the opposite way had a blow-out and crashed head-on into the bus. The driver lost control of the vehicle , which crossed the median and struck the westbound bus, Wilson told reporters.
Twitter videos were shared showing TVG's on-air coverage of a race at the track and an announcer could be heard shouting "there is gun fire at the track".
We are aware of an ongoing San Diego Sherriff's Department investigation into an incident on the Del Mar Fairgrounds today in advance of a concert featuring the artist Ice Cube.
"As is our special events protocol, substantial law enforcement and private security was on site in anticipation of the event", Del Mar Thoroughbred Club said in a statement.
Shots rang out at the crowded venue around 7 p.m. "The involved deputies were not injured".
Russian Federation to hold 'large-scale' drills in Mediterranean
With rebels defeated in most of Syria, such an offensive could prove to be the last big battle of the civil war. Russian Federation has provided crucial military support for Syrian government forces.