Crennel served as the team's assistant head coach this past season.
Before Vrabel took over as defensive coordinator this past season, Crennel oversaw the defense the previous three years and his unit never ranked below 11th in the NFL in points per game. In 2016, the Texans were No. 1 in the NFL in fewest yards given up per game after being ranked No. 3 overall in 2015.
At the end of the 2016 season, Crennel's contract expired, and he agreed to stay on as an assistant head coach.
Crennel has plenty of NFL experience that spans 50 years on the sidelines.
The well-traveled coach has spent time with the Cleveland Browns and Kansas City Chiefs as their head coach. He also was the defensive coordinator with New England from 2001-2004 when the Patriots won three of their five Super Bowls.
Besides officially announcing Crennel as the defensive coordinator, the team announced Brad Seely as the special teams coordinator, and Anthony Midget was promoted to secondary coach.
The team also announced the hires of Danny Barrett as running backs coach, John Pagano as senior defensive assistant/outside linebackers coach, D'Anton Lynn as assistant secondary coach, Matt O'Donnell as defensive quality control coach and Luke Richesson as senior director of sports performance.