"Like every decision, it comes down to what's best for the team and what gives us the best chance to win," coach Ken Whisenhunt said in a statement released by the team.
Pendergast, 41, was hired by Dennis Green in 2004 and stayed on when Whisenhunt took over in 2007.
"He was one of the guys retained from the previous staff and has done a good job," Whisenhunt said. "But as part of the evaluation process that's done after every season, I took a look at the last two years as a whole and felt this move was necessary to help us continue the progress we've made."
The Cardinals ranked 19th in the NFL in overall defense in the regular season, giving up 331.5 yards per game. They were 22nd in pass defense and 16th against the run.
The next step is for the Patriots to send Cassel a contract. Cassel effectively will not become a free agent Feb. 27 and can't shop himself to other teams. The Patriots could still trade Cassel.
Jurisprudence:: Three Houston police officers accused of beating the father of Packers wide receiver Donald Driver have filed a defamation lawsuit, saying Marvin Driver Jr. and activist Quanell X made false statements about the November arrest.