Dom Capers has seen this scenario unfold in nearly every NFL training camp he's experienced.
Whether it's through injury or performance, the Green Bay Packers' defensive coordinator has watched as veterans give way to young players during the month-long gauntlet.
Three weeks into camp, this year is no exception.
"That's kind of the way this game is," said Capers, who has worked in the league since the mid-1980s. "If one guy is down, another guy's reps are going to go up and he's going to get more opportunities to show what he's capable of doing."
The circle of life collected an early casualty this week when the Packers traded 2012 second-round pick Jerel Worthy to New England for a conditional seventh-round pick. He's the fourth linemen from last year's 25th-ranked defense not to be retained.
Injuries have forced both Worthy (back surgery) and seventh-year veteran Letroy Guion (hamstring) into neutral since the start of camp. In their absence, a number of young defensive linemen have emerged.
Worthy, coming off reconstructive knee-surgery, played in only two regular-season games last year before sustaining a back injury during offseason training, which required surgery and forced him to miss his second consecutive offseason program.
Finally, Packers general manager Ted Thompson decided he couldn't wait any longer.
"You know, injury situations are tough and sometimes decisions like that have to be made," Packers coach Mike McCarthy said. "And that's really my view of what happened to him. You look at a lot of careers in the National Football League, a lot of great players, their opportunity started when somebody else was injured. So, it's a big part of being successful in this league."
The Packers changed their philosophy on the defensive line this offseason. They've moved away from the two-gap scheme in which burly linemen are responsible for absorbing blockers and allowing their linebackers to make plays behind them.
Instead, they're calling on younger, more-versatile linemen to produce in an aggressive, attacking structure, which veteran nose tackle B.J. Raji said played into his decision to re-sign in Green Bay.
There's still room for the big guys, but the days of spreading 330-pound behemoths like Ryan Pickett and Johnny Jolly across the defensive line appear to be over. Now, they're asking incoming rookies like Carlos Gray to actually drop weight.
Gray left North Carolina State after his redshirt sophomore year despite starting only four games and being told by the NFL advisory committee he would be a seventh-round pick. When asked about his decision to enter the draft, Gray said: "I felt like this is where I needed to be."
He played as heavy as 340 pounds with the Wolfpack, but dropped to 320 at the time of the NFL draft and now is roughly 310. His goal is to get down to 300. Another undrafted rookie who's turned heads inside the organization, Colorado State-Pueblo's Mike Pennel, performed hot yoga this offseason to trim down.
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"I believe it's just something that they want to be smaller so we can move and run faster," Gray said. "The past few D-lines they've had have been very big guys. They were more of a gap defense. Now they're more of an attack defense. They need guys who can move."
The Packers hoped Worthy could be one of those guys when they traded a second- and fourth-round pick to move up eight spots to draft him 51st overall two years ago. However, his quick jump off the ball resulted in more false starts than sacks in Green Bay.
His latest injury wiped out a second chance at harnessing that ability, so the Packers moved on. They drafted Datone Jones in the first round last year and watched 2012 fourth-round pick Mike Daniels evolve into the pass-rusher they hoped Worthy could be.
Fifth-round pick Josh Boyd saw his role swell as last season wore on. Initially seen a fringe player during last year's cut downs, he was seeing more snaps than Jones by season's end.
Guion and Worthy's inactivity allowed Pennel (6-4, 332) and third-round rookie Khyri Thornton (6-3, 304) to get extended snaps in Saturday's preseason opener against Tennessee. In Pennel's case, he was the first off the bench to replace Raji at nose.
"Those two guys being hurt, those young kids have gotten a great opportunity that maybe they wouldn't have gotten without the injuries," Packers defensive line coach Mike Trgovac said. "They've taken advantage of it."
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McCarthy suggested Thursday that Guion is nearing a return from the hamstring injury he sustained a week before camp. He'll travel to St. Louis this weekend, but won't play against the Rams.
Guion signed for a one-year deal with a $100,000 signing bonus in March and was seen as a rotational lineman, who also could spell Raji inside.
The Packers got a close look at him during his six years with the Minnesota Vikings, but the organization's growing intrigue with Thornton, Pennel and Gray means Guion won't make the roster on reputation alone.
"Letroy's been around a long time," Trgovac said. "He's played a lot of football so we have evidence on tape of him."
The Packers have drafted heavily on the defensive line under Thompson, especially as of late. He's taken at least one at the position in all 10 of his drafts and at least two on five occasions.
This year's group is lighter and younger than any of the previous incarnations, but that's not necessarily a bad thing. Something needed to change after a late-season defensive collapse.
Gone are Pickett, Jolly, veteran C.J. Wilson and now Worthy. To fill those vacancies, the Packers are counting on a core of young and determined linemen.
"You want to have maybe some older vets, but not really, because we're more relatable because we're all so young," Pennel said. "We listen to the same music, do the same things. It's just been good. It's almost like a brotherhood in the room and everything."
— firstname.lastname@example.org and follow him on Twitter @WesHod.