Halfway through the 2013 regular season, the Green Bay Packers' run defense ranked No. 5 in the NFL.
By the end of the year, it had collapsed to No. 25 and was one of the reasons the Packers finished in the bottom quarter of the league's overall defensive rankings (No. 25 in yards allowed and tied for No. 24 in points).
In the offseason, general manager Ted Thompson's personnel decisions said plenty about what he and the Packers' football staff thought was the problem, at least along the defensive line: age and athleticism.
Two 2013 opening-day starters who were key performers in the run defense's strong start in '13, Ryan Pickett and Johnny Jolly, are gone. So is four-year rotational backup C.J. Wilson.
A.J. HAWK: Tackles fan at celebrity golf tournament
Pickett, a rare Thompson free-agent signing, provided seven years of distinguished service on the Packers' defensive front.
But by the second half of last season, at age 34, Father Time finally had caught up to him.
Same for Jolly, whose stunning strong showing in training camp last summer won him a roster spot after three seasons of NFL suspension. At age 30, he wasn't the same player in the second half of 2013 as he was early, and he remains unsigned after only recently getting medical clearance after a neck injury sustained in late December.
In their stead, the key players on the defensive line will be younger and more athletic, most notably 2013 first-round pick Datone Jones, who turns 24 next week, and third-year pro Mike Daniels, who is 25.
Thompson also spent a prime 2014 draft pick, a third-rounder, on Southern Mississippi defensive lineman Khyri Thornton. And a fifth-round pick from last year, Josh Boyd (25 in August), is in good position for prime rotational work after a promising finish in '13.
With all that turnover, the old man of the line is 28-year-old B.J. Raji, who re-signed for one year after the free-agent market proved a major disappointment coming off his pedestrian 2013 performance.
"I like our young guys," said defensive coordinator Dom Capers when asked this offseason if the Packers needed to get more athletic on the defensive front. "We've got a little different look to us on the defensive line from what we've had. Having B.J. inside as a nose tackle is going to be good, and we've got a lot of young guys we're looking at."
The critical player for meaningful improvement up front in 2014 probably is Jones.
PACKERS PRO SHOP: New store designed to 'wow' fans
Thompson selected Jones at No. 26 overall last year to improve the defense's athleticism after San Francisco 49ers quarterback Colin Kaepernick set an NFL playoff rushing record against the Packers in January 2013. But what looked like a promising rookie year early last August didn't pan out.
In the first two weeks of training camp, Jones almost daily flashed a snap or two of playmaking ability but then sprained his ankle on the first defensive play of the preseason opener. He missed the next week of camp, didn't perform the same after he returned, and ended up in only a niche role as an inside rusher on obvious passing downs.
Capers estimated that Jones wasn't fully recovered from the injury until the final quarter of the season. Though Jones didn't miss a game, he took part in only 24.5 percent of the team's defensive snaps and finished with 3½ sacks.
"We're expecting Datone to take a big step this year," Capers said.
Jones' playing time figures to at least double with Pickett (46.4 percent of the defensive snaps in '13) and Jolly (27.3 percent) gone. Depending on opponent, Jones could be a starter in the 3-4 along with Raji at nose tackle, and either Daniels, Boyd or free-agent signee Letroy Guion at the other end.
Regardless of Jones' role in base personnel, he will play extensively as one of the two inside rushers in the nickel, which is by far Capers' most-used personnel group. There he will team with Raji or Daniels on run-pass downs, and Daniels or Mike Neal on longer downs-and-distances.
PACKERS HALL OF FAME: Green, Ruetters to be inducted
"I think everybody when (Jones) first came in here saw his athleticism," defensive line coach Mike Trgovac said. "He's a tough kid. There's never been a question of that. He probably fought through that (ankle) thing and tried getting on the field, being a first-round pick and all of that. His maturity in everything he does, his studying, his practice habits, everything will take a leap this next year."
Daniels, in the meantime, could be a budding standout. In his second season last year he became one of the Packers' best defensive players and was a dynamo as an undersized (6-0 and 300 pounds) inside rusher. His 6½ sacks ranked sixth in the NFL among interior rushers.
"People were probably a little bit afraid of (drafting) him because of his size and his height, and he doesn't have the NFL standard height and arm length," Trgovac said. "But we really loved him. He's an ex-wrestler who will get in there and grapple with (offensive linemen). He's not going to be a finesse guy. He's very tough, works hard, great leverage and very good hands."
Daniels' high-energy effort and extroverted personality also bring an edge to the defense.
"He's got a real good defensive temperament," Capers said. "He's a tough guy, a guy you can count on to give you everything he's got every down."
The Packers are hoping that Raji's move to full-time nose tackle in their base personnel will rejuvenate him after watching his play slowly decline from 2010, when down the season's stretch he was one of the key players in the Packers' run to the Super Bowl title.
For the last three years the Packers have insisted that despite Raji's diminishing production he wasn't miscast playing mostly at end (with Pickett at nose tackle). But they drafted him No. 9 overall in 2009 as a nose tackle for Capers' scheme and now are projecting him to be better in that role than he's been the past couple of seasons.
"When we had him and (Pickett) on the same team — both good football players — you don't want one sitting on the bench," Trgovac said. "I think (nose) is his natural position."
This could be a make-or-break training camp for another young defensive lineman, 2012 second-round pick Jerel Worthy. The Packers generally keep only six or seven defensive linemen on their 53-man roster, and Worthy enters camp on the bubble after a quiet and injury-diminished first two seasons in the league.
AARON RODGERS: Odds to win golf tournament? 50-to-1
The Packers used a premium draft pick on Worthy mainly because of the quickness he showed as an inside rusher at Michigan State. He had a quiet 2½ sacks as a rookie before sustaining a torn ACL in the 2012 regular-season finale. He then missed the first 10 games last year while recovering, played only 11 defensive snaps after his return, and missed all offseason practices this spring because of an undisclosed injury.
"Last year was just a lost year." Capers said when asked what he thinks he has in Worthy. "So we'll have to wait and see."
Boyd, a fifth-round pick last year, didn't work his way into the playing rotation until late November but did enough (eight tackles in the final four games) to suggest he could be a regular after a full offseason in the Packers' workout program. Thompson also signed the former Minnesota defensive tackle Guion (age 27) to a one-year deal in free agency with the length (6-4) and size (314 pounds) of a prototypical 3-4 defensive end.
"(Guion) will give us a good rotation in there," Trgovac said. "He's a big kid that can move that's got good fundamentals. He's a taller and he's a longer-armed guy that can get that arm out there and keep guys away from him. He's a good football player."
— email@example.com and follow him on Twitter @PeteDougherty.