If you’re worried about the level of play in the NFL, you have an unlikely ally: coaches and executives. "Everything from defensive linemen not knowing where their eyes should be looking, not knowing where blocks are coming from," said Baltimore Ravens head coach John Harbaugh. "Defensive backs not recognizing routes, not knowing how to burst, stop, start, and change direction so they don’t tear their ACLs. Offensive linemen not knowing where blitzers are coming from. Just not a lot of technique anywhere."

It’s rare for NFL coaches and executives to agree en masse on anything, but these days, nearly all of them seem to be fretting about a new and game-changing trend: The NFL is getting dangerously young due to changes at both ends of the age spectrum, with record numbers of less experienced rookies entering the league and veterans getting the boot.

"This is a real serious concern," Harbaugh said. "Not just for the quality of the game, but for the well-being of these young guys coming into the NFL."

Football Outsiders tracks a statistic called "Snap-Weighted Age" that averages the age of the players on the field based on snaps. In 2015, the league-wide average age hit its lowest mark since the site started keeping track a decade ago. In 2006, the average age of the players on the field was 27.2; in 2015, it was 26.6. On offenses alone, the average age of players on the field dipped almost a full year, from 27.6 in 2006 to 26.8 last year.

That’s partially because teams are now less inclined to keep aging players around. Despite medical and nutritional advancements, NFL careers are ending earlier for anyone who isn’t a quarterback or a special teams cog. In every year since the NFL/AFL merger in 1970, a 36-year-old offensive lineman had appeared in a game — until last season, when there were no 35-year-olds, either. Last year, the number of offensive linemen age 28 or over who appeared in a game dropped nearly 20 percent compared to 2011, while the number of players age 31 or older at any position fell 20 percent from a decade ago.

It’s also because rookies are flooding the league. This year’s draft featured 107 early entrants, easily a record. Last season, 25 players age 21 or younger appeared in an NFL game, five times as many as in 2000 and more than double the total in 2012, a year after the league’s latest collective bargaining agreement was struck.

In February, The Wall Street Journal reported that the average career length for NFL players has shrunk by two and a half years since 2008, and that shift is a source of great anxiety for coaches. "Let’s be honest, the younger the league, the less experienced the league is and with that, the quality of play doesn’t start off at the same level," said Packers head coach Mike McCarthy. "I think what you see, particularly in the early part of the season, is a reflection of that."

McCarthy is particularly concerned about the end of veteran lines, which were staples of the league when he entered as an assistant in 1993. His Packers didn’t play an offensive lineman older than 29 last year — and that 29-year-old was Josh Sitton, who the team released last weekend.

Despite coaches’ concerns, though, a collision of forces has made the age trend too fierce to counteract. The short version: In the past five years, NFL teams have committed heavily to cost-effective rookies, reserving lucrative second contracts for the game’s biggest stars. At the same time, the number of third-year juniors leaving college has swelled due in part to what Steelers general manager Kevin Colbert said is accelerated physical development and in part to a desire to get to the second, big-money contract sooner despite the low odds of most players actually cashing in. And though many of those early entry players are great talents, they face a steep learning curve when they enter the NFL. Because of strict roster limits on the number of players a team can carry and an uptick in the number of packages that rely on extra personnel, it’s now far harder to hide a less prepared draft pick on a roster — and that creates problems on the field. Further complicating matters, coaches and executives think rookies are less prepared than ever, but the new CBA restricts padded practices and offseason contact between players and coaches, limiting learning opportunities. Looming over all of that is teams’ reliance on the rookie salary scale, which since the 2011 CBA has guaranteed teams access to cheap players for four years and created a world in which older players have to break out in a big way to stick around after their first deal expires. And yes, that’s really the short version.

"It’s just a fact, you have to continue to load your team with younger players, in hopes they are ready to go and ready to play productive football," Bengals head coach Marvin Lewis said. "And yet, they are staying less in college, the rules are prohibitive, and [college] coaches are spending less time with players in college. The process from the bottom-up is shrunk, and you have to try to move them forward as quickly as you can."

Of course, moving quickly may be the problem.

"We’ve got a list," said Buffalo Bills general manager Doug Whaley, "of six positions we’re going to pay." The positions: quarterback, left tackle, and a playmaker on offense; a cornerback, a pass rusher, and a playmaker on defense. There are 22 starters on a football field, and the Bills’ strategy calls for paying big money to six of them. The team has more than six significant veteran contracts on the books at the moment because it stockpiled assets while long avoiding paying a franchise quarterback, but "When Tyrod [Taylor’s contract] hits," Whaley said, "we won’t be able to have extra guys. The rest is up for us to draft well to replenish the rest of the roster, or find free agents who are very, very cost effective. Because you just can’t pay everyone."

Many teams around the league share the Bills’ general vision for paying big money to only a handful of veterans, and that’s a major reason the league has gotten so young. When the CBA ushered in the rookie salary scale in 2011, few understood the roster-building consequences. Previously, high draft picks had received richer contracts than basically anyone else in the league despite never playing a down, but teams wanted rookie contracts to be cost-controlled so that they could save the big money for veterans. When the old system was erased, rookie salaries plummeted.

Related How NFL Teams Spend Their Money

Sam Bradford, the top pick in 2010, signed for a guaranteed $50 million. Six years later, top pick Jared Goff signed a deal worth $27.5 million. After the new CBA, the rookie bargains became so extreme that a new strategy was born: Collect as many good rookie contracts as possible and use the spare cap space to splurge on a handful of second contracts. In today’s NFL, a second contract usually means a massive jump in money. Broncos superstar pass rusher Von Miller made salaries of $1.3 million and $1.5 million in 2012 and 2013 due to the constructs of the standard rookie deal he signed. His new contract, signed this year, will pay him $114.5 million over six years. Colts receiver T.Y. Hilton, meanwhile, made $1.45 million in his first three years in the league, a steal for a player who became a Pro Bowler. His second contract called for a $10 million signing bonus and $65 million overall. Teams are using their cap space on these deals selectively and leaning on cheaper, younger players for the rest of their roster, leaving the oldies vulnerable and bringing down the average age of the bulk of NFL teams.

Related The Case for NFL Superteams

"The way the CBA is structured now, it’s really no different from any other workforce in that you want to find the healthiest, youngest, least-expensive talent and infuse it into your corporation," said Titans general manager Jon Robinson. "We’re the same model."

And so the churn rate for older NFL players gets faster. If draftees don’t adjust to the pro game quickly, their NFL careers can be over in short order. The reality, Whaley said, is that less college experience means a longer adjustment to the NFL game, but players are due for extensions after four seasons (except first-round picks, who have team options for a fifth year), often before things have really clicked. "These guys coming in now may not be ready until Year 3," he said. "And you’ve got to pay him and you have no idea what to do with him."

Sometimes, teams figure, it’s easier to let those guys go.

"Look at Josh Norman," Carolina Panthers coach Ron Rivera said. "He was young. He fought the system, he was a maverick, did things his own way."

Norman entered the league in 2012 as a fifth-round pick from Coastal Carolina. He was a late bloomer who never attracted much attention from big colleges and flashed athletic ability but little more in his first two seasons in the league. "But [secondary coach Steve] Wilks was patient," Rivera said. "[Defensive coordinator] Sean McDermott was patient. We kept fighting with him and in 2014, he buys in all of the sudden. All of that athletic ability came together with what he was learning and you finally saw the skill."

Rivera details this particular case because Norman developed into one of the best cornerbacks in the NFL during his age-27 season and a year later was a key piece for the Panthers during their run to the Super Bowl. He is also, Rivera observed, the type of project that NFL teams increasingly have little time for. "A lot of guys we get are tremendous athletes but their skill set hasn’t been fixed," he said. "There’s no patience."

Panthers general manager Dave Gettleman said that the sport has changed dramatically because of the combination of less developed player skill sets and a lack of patience from teams. He cited Bill Walsh’s seminal book, Finding the Winning Edge, which stated that from the moment a player (or coach or employee) enters the building, he has two years to prove his worth. This has long been established conventional wisdom throughout the league, but suddenly, it’s become problematic.

"Now, because the players are not coming as ready to use, you have to give him the third year," Gettleman said. "But there’s no patience."

No team has had more success with young players in recent years than the Panthers, as Cam Newton, Kelvin Benjamin, Luke Kuechly, Kony Ealy, and Devin Funchess all jumped to the league early and helped build one of the NFL’s best squads. Yet despite their success, the Panthers still worry about the vast youth movement spreading through the league.

Rivera cited footwork as a specific concern for today’s rookies. He’s troubled that young cornerbacks tend to backpedal with their bodies half open instead of facing the receiver and that new linebackers throw their bodies into plays to recklessly tackle, often leading to a missed tackle or an injury. He’s worried that the new breed of receiver runs limited routes in college.

To account for this, Rivera has a two-pronged approach for young players: For the freak athletes who have the talent to play right away or those who are forced to play right away due to a lack of positional depth, he uses training camp to immerse them immediately, even pairing them with a veteran in their position group to create a culture of staying after practice, something he said has been crucial in the post-2011 CBA era of limited practice. For raw talents, he eases them in slowly while still stressing that all young players get reps with the first team so that coaches can better gauge their development. He uses Andrew Norwell, now one of the league’s best guards, as an example of a player he opted to bring along slowly, but still gave the occasional look at first-team guard before he was really ready.

"Everyone’s skipping certain elements of development," said Rivera, who expects to see more draft busts as teams base player selection off what he calls "one-year-wonder" juniors. "There’s so much of this going on that you do wonder where these guys are being developed."

On March 18, 23-year-old Ravens cornerback Tray Walker died from injuries suffered in a motorbike accident in Miami one day prior. Eight days later, at the funeral in a Baptist church in south Florida, Harbaugh approached the head of the NFL Players Association, DeMaurice Smith. "I said the rules have to be adjusted for first-, second-, third-year guys," Harbaugh said, referring to rules that limit offseason contact between players and coaches. "The rules are built for guys who have families and need time off."

Smith said the interaction was brief. "One, we were at a funeral," he said. "Two, we don’t negotiate with coaches. If he has any issues he has an owner right upstairs. The owner reports to the management committee and they approach us about changes." Smith said that over the life of the now five-year-old CBA, owners have not made a proposal about changing offseason procedures.

"We’d always be open to changes or discussing it if coaches abided by the rules we already had," said Smith. The Ravens were forced to cancel one week of offseason activities for not following those rules, putting rookies in pads during a period when doing so was prohibited.

Harbaugh is concerned about what a younger NFL means for the on-field product, but also for the sport’s ability to deal with players off the field. He thinks the influx of youth has created an atmosphere in which there’s a greater need to keep players in the building in the offseason in an effort to make sure they’re behaving smartly. He said he’s currently "vetting the CBA" to figure out if he can send team employees to work out with players at their homes.

"I think about it all the time," Harbaugh said of Walker’s death. "Maybe one of our guys goes into the garage, maybe we see the motorbike. We say ‘What’s this all about? Is this really safe?’"

When it comes to strictly football matters, Harbaugh thinks the league and the union are failing younger players. "If you want to become a great piano player you’ve gotta play piano. If you want to be a great golfer you’ve got to play every day. But if you want to be a great football player, it’s ‘Oh, we aren’t allowed to play football for three months,’ and I don’t even mean play football, I mean we can’t do a drill. It doesn’t make sense."

The modern NFL rookie is a paradox, said Phil Savage, executive director of the Senior Bowl and a longtime NFL executive. "The résumé of a college player used to be much thicker. The height, the weight, the speed, and the skill ability has far surpassed what it used to be. But the technique of playing the sport is probably lacking."

Due to his position at the Senior Bowl, the premier college scouting game held annually in Mobile, Alabama, Savage watches college players closely throughout the season. He said that while plenty of the rawness incoming players carry can be traced to the 1991 NCAA rule that limited practice to 20 hours a week per team, the dip has worsened in the past few years. There’s the spread offense, of course, which has been well-documented as a thorn in NFL coaches’ sides. Whaley expressed frustration at college offenses that lack huddles and playbooks. "The college quarterback is a joystick, and the coach is playing the joystick," he said before going on to echo Savage: "A lot of these guys are taught scheme and not technique."

There’s also the matter of teams taking it easier during spring practice, limiting tackling or two-a-days in order to keep players fresher, and Savage believes that change has cost young players. "Look at edge pass rushers, outside linebackers," Savage said. "A lot of them are one-trick ponies in college. They rely on speed, then they go to the NFL and get locked up and they don’t have a counter move. They can’t get reps at full speed, you can’t replicate this stuff in practice, and then when it’s a real game it’s very difficult."

Vikings general manager Rick Spielman said one trend that exacerbates that rawness is the tendency for coaches to switch players’ positions during their college careers. Increasingly, slower but physical safeties are becoming linebackers, bigger and slower linebackers are becoming defensive linemen, and less-athletic defensive linemen are becoming offensive linemen. This creates a challenge in scouting and development, Spielman said; however, he said that college coaches can occasionally be vindicated, like in the case of second-year Vikings offensive tackle T.J. Clemmings, a fourth-round pick and defensive end-turned-OT, whom the Vikings were able to quickly turn from a raw product into a productive member of the team.

Whether coaches or executives can point to a similar success story, they’ve all arrived at the same conclusion: This trend isn’t stopping, meaning NFL teams need to learn to live with a league full of 21-year-olds and light on those on the wrong side of 30.

"All of the underclassmen, that number is ever-growing and it’s not slowing down," Robinson said. "Some of them are prepared for the National Football League, some of them are not. We have to figure that out quickly."