While the move may have hindered his draft chances,[citation needed] it increased his knowledge of the game, by experiencing the trenches from both the offensive and defensive side of the football.

When Parcells stepped down as Giants head coach after Super Bowl XXV, Crennel stayed with the team under the two-year tenure of Ray Handley.

He was not offered any jobs and was passed up by the New York Giants, Buffalo Bills, Arizona Cardinals, Chicago Bears, and Atlanta Falcons.

[10] On November 5, 2012, Crennel announced he would be stepping down as defensive coordinator and named linebackers coach Gary Gibbs to the vacant position, after a 1–7 start to the season.

[11] On December 1, 2012, Crennel attempted to prevent the suicide of player Jovan Belcher by talking to him and witnessed his death by a self-inflicted gunshot wound to the head.

[14] On January 20, 2014, Crennel signed a 3-year deal with the NFL's Houston Texans becoming their new defensive coordinator under their new head coach Bill O'Brien.

On January 20, 2018, he returned to his role as defensive coordinator for the Texans after Mike Vrabel left to become head coach of the Tennessee Titans.

Crennel was named the interim head coach for the Texans on October 5, 2020, after O'Brien was fired following an 0–4 start to begin the 2020 NFL season.

[17] Crennel also became the Texans' first African American head coach in franchise history, albeit on an interim basis.

[19] * – Interim head coach Crennel had hip replacement surgery in early 2009 and decided to sit out the 2009 football season while recuperating.