A frustrating defensive era for East Carolina football came to an end on Thursday, when head coach Ruffin McNeill announced he was not renewing the contract of defensive coordinator Brian Mitchell.

That decision marked the end of a three-year ride for Mitchell and the ECU defense characterized by lots of promise, sprinkles of game-changing plays but overall a mass of yards and points allowed, even in the defense’s second season after switching from a 4-3 scheme to a 3-4.

McNeill said on Thursday the search for Mitchell’s replacement already is under way, and he declined further comment on the situation until a new hire is made. The head coach was in Greenville on Thursday but was expected to leave early this morning for a recruiting visit.

“There’s never a good time to make a coaching change, especially one that involves a friend and colleague who I respect professionally,” McNeill said in a statement. “However, I have the responsibility and commitment to maintain the best interest for this program and East Carolina University.”

In his final season as both coordinator and defensive backs coach, Mitchell’s unit was shelled for 5,559 total yards (430.69 per game) and the Pirates fell from 56th nationally in total defense in 2011 to 87th this year.

After a dreadful end to their first season together in 2010 — the Pirates lost five of their last six games and were outscored 325-220 in that stretch — McNeill and Mitchell agreed on the switch to a 3-4.

With budding stars like linebacker Jeremy Grove and linebacker/end Derrell Johnson, the change produced drastic results in ’11, but they were not matched this season with a more experienced team.

The team’s worst two games in terms of yards allowed were the last two of the season.

After yielding 591 yards in ECU’s loss to Louisiana at the New Orleans Bowl — the fourth time this season the Pirates allowed more than 500 yards — McNeill indicated he would be evaluating his defense but did not specifically address his coordinator.

Mitchell came to ECU after spending four years as cornerbacks coach at Texas Tech and 11 previous seasons as an assistant at his alma mater, Brigham Young.