The firing came one day after general manager Phil Savage was dismissed. Owner Randy Lerner met with Crennel on Monday morning and the team announced the coach's firing moments before a news conference was to begin.
Crennel had three years left on a contract extension he signed in January after the Browns went 10-6 and just missed the playoffs.
Crennel went 24-40 in four seasons with the Browns, who entered 2008 with huge expectations but collapsed amid a series of injuries and uneven play on offense and defense. They didn't score an offensive touchdown while losing their last six games and posted their fifth season of at least 10 losses in six years.
Although Crennel's dismissal had been expected for some time, Lerner waited until after the season out of respect for the 61-year-old coach and former defensive coordinator, who had never been a head coach at any level before taking over the Browns in 2005.
Lerner is expected to make a strong run at former Pittsburgh Steelers coach Bill Cowher, who has been working as a studio analyst for CBS since stepping down following the 2006 season. Cowher has given no indication he is ready to return to coaching.
Crennel was regarded as the top coordinator available when the Browns hired him shortly after they brought in Savage. Crennel accepted Lerner's offer in the hours after winning his third Super Bowl as New England's defensive coordinator. Crennel won two previous Super Bowl rings as an assistant coach with the New York Giants.
Crennel's vast experience, defensive knowledge and even-keeled demeanor were vital at the time for the Browns, who were coming off a 4-12 season under Butch Davis. Cleveland went 6-10 in Crennel's first year and just 4-12 in 2006, when they lost six of their last seven games.
But after a 10-6 season in 2007, Crennel was given the contract extension through the 2011 season. With an explosive offense and six Pro Bowlers, the Browns were tagged as one of the league's rising teams entering '08. They were rewarded with five prime-time TV appearances but their schedule proved to be too much.
They were also ravaged by injuries as quarterbacks Derek Anderson and Brady Quinn were lost for the season, forcing Crennel to start recently signed Bruce Gradkowski in the season finale at Pittsburgh. The Browns were beaten 31-0, dropping Crennel to 0-8 in his career against the Steelers — the only full-time Browns coach not to beat Cleveland's rival.
Crennel was genuinely respected by the Browns. The players referred to him as RAC, his initials, and were disappointed they didn't play better for him.