Throughout another unfulfilling Buffalo Bills season, new defensive coordinator Mike Pettine's work was a glowing highlight.
Flip that switch.
Pettine's gone, and for the fifth time in six seasons, the Bills will name another defensive coordinator.
The Cleveland Browns just announced they have hired Pettine to be their new head coach.
The Bills must regroup. Pettine could take some of his assistants with him to Cleveland. Linebackers coach Jim O'Neil, defensive line coach Anthony Weaver and assistant secondary coach Samson Brown came to the Bills with Pettine from the New York Jets.
Bills General Manager Doug Whaley said at the Senior Bowl in Mobile, Ala., the front office has a list of coordinator candidates ready to go and would begin the search to replace Pettine immediately.
The only position coach on the Bills' staff with previous NFL defensive coordinator experience was secondary coach Donnie Henderson. He ran the Detroit Lions' defense in 2006 and the Jets' in 2004 and 2005.
The most notable defensive minds looking for work are former Bills coach Wade Phillips, former 49ers coach Mike Singletary and two recently fired head coaches, Jim Schwartz of the Lions and Greg Schiano of the Tampa Bay Buccaneers.
Former St. Louis Rams coach Steve Spagnuolo is a special assistant for the Baltimore Ravens. Former Browns and Jets coach Eric Mangini is a San Francisco 49ers consultant. Each could be interested in being a coordinator again.
Respected assistants who could be ready for promotions include 49ers defensive line coach Jim Tomsula, Seattle Seahawks passing-game coordinator Rocky Seto, Pittsburgh Steelers linebackers coach Keith Butler and Minnesota Vikings defensive line coach Brendan Daly.
Linebackers coach Pepper Johnson left the New England Patriots on Tuesday.
Browns fans certainly will view Pettine as an unproven commodity, something they've grown disgusted with over the years. The Browns fired Rob Chudzinski after one year. Before him, Pat Shurmur was a rookie coach who lasted two seasons.
Bills fans, however, are disappointed to see Pettine leave. He's the first Bills assistant to become another team's head coach since the Indianapolis Colts hired Ted Marchibroda 22 years ago.
Buffalo was a wreck before Pettine arrived. Previous defensive coordinator Dave Wannstedt ran a stale, passive 4-3 scheme that got trampled on a weekly basis.
Pettine took essentially the same defense and morphed into a decorated unit that caused opponents trouble every week.
Four of the Bills' 11 starters -- pass-rusher Mario Williams, defensive tackles Kyle Williams and Marcell Dares, safety Jairus Byrd -- were selected for the Pro Bowl. Inside linebacker Kiko Alonso, is a top candidate for defensive rookie of the year.
Pettine helped salvage a few careers, too. Players who looked like busts enjoyed remarkable seasons, namely pass-rusher Jerry Hughes, cornerback Leodis McKelvin and safety Aaron Williams.
Atlanta Falcons quarterback Matt Ryan declared the Bills fielded one of the NFL's elite front-seven units. Buccaneers defensive tackle Gerald McCoy praised Kyle Williams and Dareus as the best interior duo.
The Bills ranked 10th in total defense, 28th in run defense and fourth in pass defense.
They were gashed for long runs, allowing a league-high 19 rushes of 20-plus yards, but they hardly resembled themselves from the previous season.
The 2013 Bills were aggressive and dangerous. They set a club record and ranked second in the NFL with 57 sacks. They were second in interceptions.
The Bills allowed only seven defensive touchdowns against the Browns' AFC North opponents, which included the defending Super Bowl champs, the eventual division champs and the Pittsburgh Steelers at Heinz Field.
Ravens quarterback Joe Flacco throw a career-worst five interceptions against them. The Bills should've beaten the playoff-bound Cincinnati Bengals, but lost in overtime.
The Bills lost to the Browns, but not for defensive reasons. Bills quarterback EJ Manuel suffered one of his knee injuries, and the Browns scored on a punt return and a Jeff Tuel interception.
But many at One Bills Drive and around the league are surprised Pettine is getting a shot to be head coach so quickly.
Just a year ago, he struck out on his own. He was Rex Ryan's sidekick for 11 years, breaking into the NFL with an entry-level job on the Ravens' staff in 2002. Ryan was a Ravens assistant at the time. The two grew close.
When the Jets hired Ryan in 2009, he brought Pettine with him. Although Pettine was the Jets' coordinator for four years, Ryan truly ran the defense.
Pettine runs a version of the 46 defense Buddy Ryan introduced with the Chicago Bears three decades ago.
The 46 didn't catch on at the time but has the past couple years through Buddy Ryan's sons and their protégés. Rex Ryan fields a strong unit each year with the Jets. Rob Ryan improved an historically bad New Orleans Saints defense into one of the league's best in 2013.
Bob Sutton, the Jets' linebackers coach under Pettine, installed a 46 scheme with the Kansas City Chiefs this season. Sutton's defense propelled the Chiefs from a 2-14 record to the playoffs in one year.
Given the complexities of the 46 defense and the fact Pettine has been learning about it for the past dozen years, he brings an intriguing background to the table few other candidates can match.