Gun shots were fired Sunday afternoon near the Del Mar race track north of San Diego.
The sheriff's office said the suspect was "down" and had been taken to hospital. "Deputies engaged and returned fire", the statement said.
The sheriff's department said the alleged gunman shot by deputies was taken to Scripps Memorial Hospital La Jolla.
Video provided by Fox San Diego showed deputies struggling with a man in a white shirt on the ground.
Witnesses said the man had fired three shots and that sheriff's deputies had tried to stop him with a Taser before opening fire, CNN affiliate CBS 8 reported.
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.
The race track later tweeted that the situation was contained, and the concert would go on as scheduled.
In a broadcast of the track's final race of the day that was posted on Twitter, an announcer can be heard saying, "There's gunfire at the track", as horses move along the turf course, the Union-Tribune reported.
There were 18,000 people on hand for the Summer Concert Series at the Del Mar Fairgrounds.
As is our special events protocol, substantial law enforcement and private security was on site in anticipation of the event.
Del Mar's official Twitter account said at 6:37 p.m. PT that the concert was officially "sold out".
Ambulances and helicopters were also seen shortly after the shooting.