PHILADELPHIA >> Juan Castillo’s offense-to-defense coaching experiment backfired in Philadelphia, costing the defensive coordinator his job.

Castillo was fired by Eagles coach Andy Reid on Tuesday and replaced by secondary coach Todd Bowles. It was the first time Reid dismissed a coach midseason in his 14 years in charge.

“I put Juan in this situation and things didn’t work out the way I had hoped,” Reid said. “I take full responsibility for putting him in that situation.”

Reid’s decision last year to promote Castillo after 13 seasons as offensive line coach was a stunner. It came after a long search and with new defensive line coach Jim Washburn already in place running a wide-nine scheme that isn’t widely used.

Castillo was under the microscope right from the start, with nearly every move he made scrutinized intensely. He seemed overmatched in his first season and the defense struggled as Philadelphia started 4-8. But Castillo’s unit showed enough improvement during a season-ending four-game winning streak that he stuck around.

Until now.

“I have to do what I think is right whether it’s with public opinion,” Reid said, “or against public opinion.”

The move came two days after the defense blew a 10-point lead with 5:18 remaining and lost 26-23 in overtime to Detroit. A week earlier, the defense allowed Pittsburgh to rally for a winning field goal in the final seconds.

The Eagles (3-3) are on a bye this week, and Reid hinted more changes could be coming. An offense that features several dynamic players is next-to-last in scoring and turning the ball over in bunches.

“Please understand that offense, defense and special teams right now, we need to get better,” Reid said. “I’m going to continue to work through that and it’s my responsibility to do that. I’m just bringing this to you because this is what’s happened so far. I’m still evaluating.”

Does that mean Michael Vick may get benched for rookie Nick Foles?

“As I sit here today, Michael’s the starting quarterback,” Reid said.

That’s not much of an endorsement.

Reid doesn’t have much job security himself, so he’ll likely try anything to win. Team owner Jeffrey Lurie already stated in the preseason that another 8-8 season would be “unacceptable.” Lurie even said last year that he considered firing Reid after the team failed to live up to high expectations.

“You fight to win football games as a football team,” Reid said. “You try to make your football team the best possible football team they can be. You try to better yourself every day. You want your coaches to better themselves every day. You want your players to do it and you hope you have an influence on helping them become the best they can be. That’s my job and that’s how I go about doing it.”

Castillo was with the Eagles for 18 years, longer than any coach in franchise history.

“One of the tougher things I’ve had to do,” Reid said.

Castillo’s defense held the Lions in check for three quarters on Sunday, allowing just a pair of field goals. All-Pro wide receiver Calvin Johnson had one catch for 28 yards and Matthew Stafford was 7 of 21 passing.

But, according to defensive players, the Eagles inexplicably changed their game plan in the fourth quarter. They started blitzing more in an effort to pressure Stafford. Also, cornerback Nnamdi Asomugha didn’t shadow Johnson the way he did the first three quarters.

Stafford picked apart the defense, Johnson had a big day and the Lions scored 20 points in the fourth quarter and overtime.

“I was on him most of the game,” Asomugha said of covering Johnson. “I think when we got to the fourth quarter, there was a lot more trying to give him a different look.” 

Reid disputed that assessment a day later, saying “there wasn’t a great change of scheme on what we did in the first three quarters.”

Regardless, Castillo is gone.

Castillo joined the Eagles in 1995 as an offensive assistant under coach Ray Rhodes. He was promoted to tight ends coach in 1997, and then offensive line coach in 1998.

Bowles becomes Philadelphia’s third defensive coordinator since longtime assistant Jim Johnson died in 2009 following a battle with cancer. Sean McDermott had the job for two seasons and Castillo lasted 22 games.

Bowles was 2-1 as the interim head coach for Miami last season. The former Temple star played eight seasons in the NFL as a safety, including seven years with the Washington Redskins.

Bowles is in his 13th season as an assistant coach. He began his NFL coaching career with the New York Jets in 2000 as a secondary coach, spent four years in Cleveland, three in Dallas and four with the Dolphins before coming here.

Reid wanted to interview Bowles after firing McDermott, but was denied permission by Miami.

“He has a good understanding of the game, not only the secondary but the whole picture,” Reid said of Bowlers. “He gets it and he understands how to tie it all together. He’s detailed with his techniques. He relates well with the players. He’s a smart guy and he works hard. Those are normally good qualities to have.”

The decision comes at a critical time for the Eagles, who are just one game behind the Super Bowl-champion Giants (4-2) in the NFC East. New York is already 0-2 in the division, including a loss in Philadelphia last month. The bye allows Bowles time to set his strategy and move forward. He has to figure things out quickly, however, because the Eagles host the Atlanta Falcons (6-0) on Oct. 28.

“I don’t think there will be a transition period,” Reid said. “I’m not looking at that as I’m making this move. He understands it and knows it. I’m not looking for transition periods right now. I’m looking for him to step in and do his job to the best of his ability with the players that he has. I think he has good football players and good coaches around him. I expect us to do better.”

If not, Reid could be next to go.