After a disappointing and historic end to the 2009 season, there were going to be changes in the Denver Broncos’ organization. But defensive coordinator Mike Nolan, who oversaw a surprising turnaround on defense, appeared to be one of the team’s foundations.

The team’s defense will undergo a major adjustment because Nolan won’t be back in 2010. He and the Broncos agreed to part ways, the team announced Monday.

“I have great respect for Mike and wish him success in the future,” Broncos coach Josh McDaniels said in a statement released by the team.

Reports from NFL Network and ESPN on Monday night speculated Nolan could end up being hired by the Dolphins to run their defense.

The Broncos now have to start with a new defensive boss, again. Whoever runs Denver’s defense will be the fifth coordinator in five years, since Larry Coyer’s last season as coordinator in 2006.

Denver’s next coordinator will have a tough time replacing Nolan, who installed a new 3-4 scheme with the Broncos and oversaw a unit that ranked seventh in the NFL in yards allowed. In 2008, only three teams allowed more yards than the Broncos. Although the Broncos struggled near the end of last season on defense, McDaniels praised that group.

“Defensively, we played very well this year,” McDaniels said after the season. “We played together, we did our job, we kind of fit into what we asked each player to do and we didn’t really stray from that.”

Since McDaniels has called on his Patriots’ roots before, one possibility to replace Nolan might be Dean Pees, who was New England’s defensive coordinator from 2006 through last season. He and McDaniels were on the Patriots staff together for five seasons, from 2004-08. The Broncos are also looking to replace running backs coach Bobby Turner and offensive line coach Rick Dennison, who left to Washington and Houston, respectively.

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