The Eugene Police Department said they have two suspects in custody. The victim was transported to a local hospital with non-life-threatening injuries.
A video posted on Twitter appeared to show a man telling someone to put a gun away.
Wesley Hicks, an Oregon resident who was about 20 yards away from the shooting, told Fox News that security guards quickly moved in when a fight broke out.
Another witness told KEZI that the gun went off when security tackled the man to the ground, and the bullet hit a female bystander in the arm after ricocheting off the ground.
Another video posted to Facebook showed hundreds of people exiting the fair after the shooting.
The Lane County Fair, which started on Wednesday and runs through Sunday, said on Facebook around noon that they "anticipate large crowds all throughout the day."
This is a developing story. Check back for updates.