The quartet of quarterbacks contained within the NFL’s conference championship games Sunday present a generational contrast and stylistic clash. Pocket-bound throwers like Tom Brady and Aaron Rodgers once dominated the league. Today, raw athleticism is almost a prerequisite for the position, and Patrick Mahomes and Josh Allen possess it in droves. In rough outline, the foursome could form an evolutionary chart of NFL quarterback play.

The quarterbacks vying for the Super Bowl represent a broader shift. In these playoffs, nearly every quarterback fell into one of two categories: old and legendary or young and dynamic. For every Philip Rivers, there was a Lamar Jackson; for every Ben Roethlisberger, a Russell Wilson. The quarterbacks entering the league were chosen at a young age for their athletic ability as much as their passing, and they grew up in spread-out offenses that relied on both their passing and running ability. As older passers fade, they are being replaced by quarterbacks who play a different game.

Any attempt to draw a lesson from the remaining four quarterbacks demands a caveat. In their own ways, each is anomalous. Brady’s excellence in longevity is unseen in NFL history. In performance, accolades and achievement, no quarterback has started a career like Mahomes. Allen’s rapid improvement in accuracy has no precedent. Rodgers’s blend of quick release and arm strength makes him sui generis.

Still, the shift in how the position is played became undeniable this month. With Brady still thriving amid the retirement of Rivers, the expected exit of Drew Brees and the possible departure of Roethlisberger, these playoffs have felt at times like the last stand of the traditional pocket passer.

“Today’s pocket quarterback is yesterday’s scrambling quarterback,” said former NFL quarterback Chris Simms, an NBC Sports analyst. “I think that’s where the NFL is going. There’s going to be a level of expectation of the ability to get out of the pocket, extend plays, even for the pocket quarterback in this day and age. The guy like Tom Brady, that’s a dying breed. That’s the old NFL.”

Not every signal caller fits neatly under the label of “pocket passer” or “running quarterback.” But even quarterbacks who come into the league perceived as traditional throwers tend to use more athleticism than their predecessors.

“It’s almost like evolution,” Simms said. “Oh, here’s Peyton Manning from 25 years ago. Okay, now evolution has come, and now that guy is Joe Burrow. Same kind of guy. Same kind of brain in the way he throws the football. Now 25 years down the line in evolution, this guy, when there’s a hole that presents itself, this guy can rip off 30 yards with his legs. That’s a big part of the sport nowadays.”

‘You better have some athleticism’

The selection of quarterbacks at the lowest levels flipped in recent years. Youth coaches once chose the most athletic players for skill positions and tabbed bigger, slower kids to play quarterback. Now the fastest, most athletic kids are viewed as the ones coaches want to handle the ball every play. From that environment emerged, at the extreme end, players such as Jackson and Kyler Murray who are among the fastest, best ballcarriers in football.

NFL teams gravitated, then, toward mobile quarterbacks by necessity. For a chunk of the past decade, coaches lamented the difficulty of evaluating college quarterbacks who came up in the spread and turning them into pro-style passers. The ones who succeeded stopped trying to change them and instead embraced both the quarterbacks college football produced and the accompanying offensive systems. They discovered varied benefits, including how it improved the running game by forcing the defense to account for the quarterback, effectively granting them an extra blocker.

As that shift occurred, defenses grew faster and only emphasized the need for quarterbacks, especially young ones, to be able to move.

“The D-lines in this league are just ridiculous,” Arizona Cardinals Coach Kliff Kingsbury said this season. “You can’t expect to block them and hold up consistently. So if you’re not a Brees or a Brady, getting the ball out on time to the right place 100 percent of the time, you better have some athleticism to be able to extend plays.”

“You’re going to find mismatches during the year where, ‘We can’t block this team,’ or, ‘We can’t figure out this team’s blitz,’ ” Simms said. “That’s where the mobility of a quarterback in this day and age is paramount. … Not that you need to be Lamar Jackson. But you need to be at least able to get out of the pocket and make plays that way.”

The success of a quarterback in the NFL often comes down to what happens when he is presented with trouble. What does he do when a blitzer comes free? How does he handle a play when no receiver breaks open? He can solve those problems with his mind, his arm, his legs or some combination thereof. When Brady faces the blitz, he knows exactly where to find space on the field that the extra rusher left free. When Murray faces the blitz, he can juke or outrun a pass rusher.

Quincy Avery, an independent quarterbacks coach who tutors Deshaun Watson and other NFL signal callers, said young quarterbacks lack the experience to solve those problems with their mind or arm. But NFL teams lack patience to develop young quarterbacks in the pocket and have a financial imperative to play them because their rookie contracts consume a pittance of the salary cap. A young quarterback, then, must use his legs to buy time in more ways than one.

“You look at someone like Josh Allen,” Avery said. “If he’d have had the start he had from the pocket and didn’t have the ability to run, we would have never known the strides that he could make as a passer, just because they wouldn’t have given him that time to develop. They wouldn’t have moved the ball enough for them to do anything on the offensive side of the football, so he’s somebody who would be out of the league.”

Brady, Brees, Rivers and Roethlisberger redefined how long a quarterback’s career could be stretched. The current crop of quarterbacks will define the next generation of quarterback play by how they answer a new set of questions: How will dual-threat quarterbacks age, and can they develop into pocket-bound passers as time erodes their athletic skills? Will they become the next Brady and Rodgers, or will the predominance of late-30s-into-early-40s quarterbacks fade away?

“At some point, your athleticism is going to diminish just a touch where you can’t do as many crazy-special things, and maybe then that’ll be the determining thing: Where are you as a passer when that time comes?” said Hall of Fame quarterback Kurt Warner, an NFL Network analyst. “It’s going to be a fascinating trend to see. I don’t think we really know yet. I don’t think the majority of quarterbacks have been this athletic throughout the history of our game.”

‘He’s had to adjust’

Avery predicts drop-back passers will not go extinct. Instead, he expects young, athletic quarterbacks to turn into them — today’s Allen and Mahomes becoming tomorrow’s Brady and Rodgers.

He sees the process as “seamless.” As those mobile quarterbacks gain experience, they will learn on the fly how to process defenses and naturally begin to win with their arms and minds, preserving their bodies and adjusting to diminished athletic ability.

For many younger quarterbacks, the transition has already started. Watson remained an elusive runner this year, his fourth season. He still primarily operated from the pocket as he completed 70.2 percent of his passes and led the league with 4,823 passing yards.

“He’s fine no matter how you ask him to play the game,” Avery said. “Yes, it’s really cool he adds that added element of being able to run and be explosive. If he didn’t do those things right now, he’d be fine. But if he didn’t do those things as a rookie, I’m not sure we’d have looked at him the same way.”

Rodgers is now a standard-bearer for traditional quarterback play, even if he did score on a nifty scramble in the divisional round. But he once stood as one of the league’s most athletic quarterbacks.

“If you and I sat there and watched 2013-2014 Aaron Rodgers, we would go, ‘Oh, damn, I forgot how much he gets out of the pocket, dances around the pocket, extended plays,’ ” Simms said. “He’s had to adjust because he doesn’t have that luxury anymore.”

Simms added that the young passers in the AFC championship game have already begun that type of transition.

“Mahomes his first year wasn’t all over blitz packages and things like that,” Simms said. “Josh Allen, nobody’s made a better adjustment. I think we’re seeing those two guys themselves, they came into the league kind of raw, and they’re making those adjustments right here in front of us.”

New England Patriots quarterback Cam Newton offers a cautionary example. The hits he absorbed as a younger player with the Carolina Panthers led to myriad physical ailments, including a battered shoulder that required surgery and affected his arm strength and accuracy. But today’s quarterbacks are better trained to avoid injurious blows, rule changes restrict quarterback hits, and the on-field officials are more protective of quarterbacks.

“I don’t think there’s any reason why the quarterbacks coming in now can’t play into their 40s,” said former NFL quarterback Brian Griese, an ESPN analyst. “Even when these guys are running, they’re protected. You ask Josh Allen or Russell Wilson, and they know. They get what they get, and they get down. They’re not going to take big hits. There’s no reason this generation of quarterbacks can’t play much longer than previous generations.”

Avery envisioned a two-line graph, with age along the horizontal axis, one line representing football intelligence and wisdom and the other representing athleticism. He expects they will meet before the athleticism drops while the knowledge is still rising, probably around 29.

“There’s going to be a point where the athleticism is at its highest and the mental and situational awareness is at their highest,” he said. “I’m really looking forward to that time when Mahomes and Deshaun and all those guys get there. I think it’ll be really special.”

Aside from Mahomes’s victory last year and Wilson’s title early in his career, Super Bowl titles have been hogged by traditional, drop-back passers. (Brady’s existence tilts that equation.) “We’re going to get to see this trend over the next 10 years and get to answer the question: Can a more athletic quarterback truly compete for championships year over year in that system?” Warner said.

The answer already seems inevitable, to the point that in 10 years the question may be flipped: As Mahomes and Watson and all the rest turn into pocket passers, will they be able to fend off the young, mobile quarterbacks coming into the league? As those quarterbacks keep evolving, so will the position itself. By then Brady will be in his 50s, so he might not even make conference championship weekend.