On October 1, 2017, Bostic recorded a season-high 12 combined tackles (five solo) during a 46–18 loss at the Seattle Seahawks in Week 4. In Week 8, he collected eight combined tackles and sacked quarterback Andy Dalton during the Colts' 24–23 loss at the Cincinnati Bengals. On December 18, 2017, the Indianapolis Colts placed Bostic on injured reserve after he suffered a knee injury in Week 15. He finished the season with a career-high 97 tackles (57 solo), three pass deflections, and a sack in 14 games and 14 starts. His 97 tackles finished third on the team and 25th among all players in the league. Pro Football Focus gave Bostic an overall grade of 74.9, ranking 38th among all qualified linebackers in 2017.
