THE MOST important quarter of Tra Thomas' impressive career was the one he didn't play.

It was easy to forget during Thomas' retirement announcement - under the crescendo of a highlight film and in Thomas' teary words of thanks - that Andy Reid once benched Tra Thomas.

Thomas stood on the sideline, humbled, helmet in hand, for the first quarter of the 14th game of Reid's first season, at Dallas. He was hard to miss; a 6-7, 350-pound testament to potential and petulance.

Thomas, a second-year player, had taken himself out of the previous week's game with a mild groin strain. That unprofessional decision was the straw that broke Reid's back.

As he waited to enter the game, enraged and embarrassed, Thomas, the 11th overall pick in 1998, glowered.

And learned.

"It let me know I needed to be accountable for the things I was supposed to do," Thomas said. "What Coach Reid needed me to do."

The next season, he dominated.

Thomas stifled Bruce Smith. He nullified Simeon Rice. He earned a 6-year, $32 million extension in 2000, then, after the 2001 season, he went to his first of three Pro Bowls in four seasons.

That 15 minutes of punishment turned into 9 strong years as an Eagle. Thomas' likeness is carved on the Eagles' modest Rushmore of offensive linemen with Al Wistert, Bob Brown and Jerry Sisemore - all men old enough to have fathered Thomas, or fathered his father.

Generations of Eagles fans watched the team fail again and again to produce a star tackle: Kevin Allen, Antone Davis, Bernard Williams and Jermane Mayberry failed to justify their first-round selections as tackles.

Things changed with Thomas, who, after his humiliation, first immersed himself in an offseason conditioning program then sought to hone his craft with Juan Castillo, then the Eagles' line coach.

"He started studying more," Castillo said. "Before, he did things athletically. He'd say, 'Juan, just show me where the spot is. I don't have to study the guy.' As he got older, he began to enjoy doing the little things."

So much so that last year Thomas, who wore No. 72, opened a sports studio called 7 Deuce Sports in Medford, N.J., that specializes in grooming young linemen.

So much so that Thomas, on Thursday, told Reid he would tutor anyone, any time; that he one day might enjoy trying to coach, the way former standout running back Duce Staley has done the past three seasons.

It was behind Thomas that Staley recorded his three 1,000-yard rushing seasons.

"I remember seeing him the first time and thinking, 'This guy has a chance to be all-everything,'" Staley said. "He definitely was the glue to the wood."

Thomas' presence helped woo free-agent right tackle Jon Runyan for the 2000 season; like turrets, they formed the foundation for the Eagles' playoff runs. Thomas' presence helped Mayberry turn into a Pro Bowl guard, as well as his successor, Shawn Andrews.

"There were some picks that didn't quite work out," Reid said. "Tra was able to solidify that. That led into Jon coming here, knowing that Tra was here."

Like any offensive lineman, Thomas' career is difficult to quantify.

He was perhaps the least appreciated of the host of Eagles stars of his era: Donovan McNabb, Brian Dawkins, Hugh Douglas, Runyan, Troy Vincent, Brian Westbrook, Jeremiah Trotter.

Indeed, his proudest personal moment came for the 3-13 team in his rookie season, when, against Kansas City, Thomas overpowered sack specialist Derrick Thomas.

Perhaps his most significant personal opponent was Smith, the Hall of Fame end, who, in the twilight of his career with the Redskins, repeatedly told Thomas that trash-talking was wasted energy.

And kind of tacky.

"He would always, after a game, talk to me, give me some pointers," Thomas said. "Or talk to me about also how to be a professional and how to just respect the game."

At the peak of his performance, Thomas said that he wanted to play for 20 years, but a surgically repaired back in 2005 helped speed his departure from the Eagles as a free agent after 2008. One lackluster season with the Jaguars and a poor preseason start with the Chargers in 2010, and Thomas' career was over.

Thomas' retirement was a homage by Thomas to the team and the coaches who formed him.

"I want to just thank Coach Reid for always being there and being like a second father figure to me," Thomas said, pausing for 30 seconds while he choked back sobs.

Tears seeped from his eyes as he continued: "I said I wasn't going to be like this coming up here. I thought I was going to be able to hold myself together, but Coach Reid always was there throughout a lot of my own personal situations, playing the game and living life. He made such a great example of what it takes to be a father, to be a husband and to even being a professional in this game."

Being a professional sometimes means getting knocked back a step to take giant leaps forward.

Reid knocked Thomas back a notch that chilly Sunday afternoon at Texas Stadium. Staley, and Thomas, and the rest of the Eagles were better for it.

"It made him stronger, mentally," Staley said. "The point was taken."