Shead originally signed with the Seahawks as an undrafted free agent back in 2012. He spent the next six seasons with the team, and made a big impact. Shead started 21 games between 2015 and 2016, and was one of the few remaining members of the team that won Super Bowl XLVIII for the Seahawks. He became a starter toward the end of the 2015 campaign, and started 15 games in 2016. Unfortunately he suffered a torn ACL in the 2016 playoffs, which derailed his career.
He only appeared in two games in 2017 as he worked his way back from the injury, and was then cut after the season. He signed with Detroit, and appeared in 12 games for the Lions last season, making one start. He was placed on injured reserve in December, then signed back with the Seahawks in July.
As Henderson points out, the Seahawks had been mostly using him as a safety this season in an attempt to have him make the team. The Portland State product ended up coming up short, and will now re-enter the open market at the age of 30.