Belichick ran with his fiancee, Linda Holliday, and they finished the half-marathon together, according to the Tennessean. Joseph Chebet won the half-marathon with a time of 1:10:36.
"It was a great run," Belichick said. "I came out to support Linda in her hometown race for her first half-marathon."
Holliday graduated from Vanderbilt University, and Belichick was born in Nashville.
But the trip wasn't just about the marathon for Belichick. He also made time to oversee a private workout from Vandy offensive lineman Wesley Johnson, the Tennessean's Jim Wyatt reported Friday.
Scott Wietecha of nearby Hendersonville won the marathon with a time of 2:25:52, and Jeannette Faber of Nashville was the women's winner with an unofficial time of 2:47:30.
The Associated Press contributed to this report.