On January 9, 2012, Crennel was named the 11th full-time head coach in Chiefs history.
[8] Three days later, Crennel announced his intent to remain as defensive coordinator during his tenure as head coach.
[9]
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.
[10]
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.
[11][12] The following day, Crennel coached his team to a 27–21 victory over the
Carolina Panthers, the Chiefs' first home victory since defeating the Packers the previous season, and the only other home win during his tenure.
[12]
On December 31, 2012, Crennel was fired as head coach.
[13]