Barrett played for Ohio State from 2013-17 and was a four-year starter for the Buckeyes. He was the starting quarterback for the bulk of the 2014 season that culminated in a national championship, though he missed the playoff that year due to an injury suffered in the final regular season game against Michigan. After that, he bounced around several NFL practice squads, but never played a regular season snap.
The Lions have plenty of ex-players on their staff, headed by coach Dan Campbell. Campbell certainly values his assistants highly, so Barrett should have a pretty supportive environment to get to work in.