A video of the shooting that was posted on Twitter records the sounds of several shots being fired before a man falls to the ground.
According to an eyewitness, deputies had just broken up a fight outside of the admission gate when a man pulled out a handgun, pointed toward the sky and shot one or two rounds into the air.
Just before 6:40 p.m., a man came to the ticket window at the Del Mar Fairgrounds at 2260 Jimmy Durante Boulevard.
Sheriffs then tasered the suspect and opened fire when tasering couldn't contain him.
The alleged shooter was reportedly taken down by police before being rushed to hospital with gun shot wounds.
A man was shot outside an Ice Cube concert, and seconds after he went down you hear a fan ask, "Can I get a refund?"
"An argument ensued", the sheriff said in a statement.More news: Syrian FM says regime will try to avoid civilian deaths in Idlib
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His condition was not immediately available.
Ice Cube, who once rapped "shotgun bullets is bad for yo' health", was due to perform at San Diego's Del Mar Racecourse on Sunday.
The gunfire happened as the final race of the day was underway, the San Diego Union-Tribune reported.
There were 18,000 people on hand for the Summer Concert Series at the Del Mar Fairgrounds.
The Del Mar Thoroughbred Club said in a statement that under its special events protocol, substantial law enforcement and private security were on site during the event.
Following the shooting, the concert moved "forward as planned", the racetrack said.
Ambulances and helicopters were also seen shortly after the shooting.