A preliminary arrest report says the 6-foot-3, 230-pound freshman was stopped early Friday for not having a working taillight on his scooter.
Officers say O'Grady had bloodshot eyes, slurred speech and an odor of alcohol on his breath. The 18-year-old had a reported blood-alcohol level of 0.099. The legal threshold for DWI in Arkansas is 0.08; the threshold for a minor is 0.02.
He was released and has a Sept. 28 court date.
O'Grady is in his first season with the Razorbacks after graduating from Fayetteville High School.
A spokesman for coach Bret Bielema didn't immediately return a message seeking comment.