INDIANAPOLIS — Tom Landry is widely credited with being the godfather of film study.

First as New York Giants defensive coordinator and then as head coach of the Dallas Cowboys, he was one of the first to pore over reels of game film, in search or tells and tendencies to exploit.

His defenses were always among the best in the NFL. It was because he was playing a different game.

At the time, many teams didn’t take measures to hide their intentions. The game wasn’t that complex. And Landry, by simply watching film and keeping track of things like which plays teams like to run in certain situations, often knew what was coming next.

Knowing often means succeeding.

At a certain point, the rest of the league figured out what he was up to, and it was forced to evolve to keep pace and survive — and eventually attempt to thrive.

These developments are tightly woven in the fabric of the game’s evolution into what you see today. Every time someone comes up with something new and it catches hold, it forces the rest of the league to change how it operates in some form or fashion.

Just like Bill Walsh’s West Coast offense altered the NFL, so did the recent trend of populating secondaries with “big” cornerbacks. Either schemes change, or the size, speed and strength requirements of certain positions shift.

Sometimes it’s both.

These are the ebbs and flows of the NFL. Offenses find new ways to exploit defenses. Defenses catch up. Offenses change again.

It never ends.

There was a time, not long ago, that Deion Jones probably wouldn’t be considered a top draft prospect. At 6-foot-1 and 222 pounds, the Jesuit and LSU product is built more like a wide receiver, safety or running back. He doesn’t fit the profile of what many once considered a first- or second-round draft pick at linebacker.

At that size and weight, it’s hard to envision him hitting a run fit alongside someone like former Baltimore Ravens great Ray Lewis.

Those days are gone. The NFL again has evolved, opening a spot on every team for linebackers like Jones — players who are lighter and quicker and possess the range needed to patrol half the field. He now fits the size, speed and skill profile coveted by many teams.

“He went from being a late-rounder to a first- or second-round pick,” ESPN draft analyst Mel Kiper Jr. said. “He probably enjoyed as monumental leap up the board as any player at a position in this draft. That’s not unheard of, but it rarely happens. If he can get his weight up to about 225 in this league, that would be fine. He can run to the ball, great sideline-to-sideline speed, tremendous range. He had an incredible year.”

Think of Pittsburgh, and the image that pops up is something associated with toughness. That’s the image of the city, and the Steelers have long reflected those values. If any team were to have big, hulking linebackers who could blow through a two-back set and get a tackle in the backfield, it’s Pittsburgh.

But a few years ago, general manager Kevin Colbert realized the old prototype for linebackers was no longer going to work. The league was changing. The game had become more spread out, and there was a need for linebackers to contribute in the passing game, especially when they get forced on a receiver.

Heading into the 2014 draft, Colbert had his eye on adding someone who could help Pittsburgh in these areas. He went with Ryan Shazier, listed at 6-1 and 229 pounds, in the first round.

His seven sacks and 23.5 tackles for a loss as a junior at Ohio State were impressive, but what Colbert really liked was Shazier’s 4.38-second speed in the 40-yard dash.

“I think the fast guys ... that’s one of the reasons we evaluated Ryan Shazier as highly as we did: His ability to play lateral football was very impressive,” Colbert said. “He could make plays that maybe a traditional run-stopping style of linebacker wasn’t able to make. That’s why we really like Ryan and we see his progress.

“So I think game speed, the ability to cover ground laterally, it’s important. Not only for the linebackers, but even your secondary people have to make plays in space because of what the offense has forced them to do.”

It used to be that linebackers entering the NFL were almost always around 250 pounds — especially middle linebackers, who are often profiled as big, hulking, muscular presences.

The size requirements appear to be shrinking. Only four of the 42 inside linebackers drafted in the past four seasons have topped 250 pounds. And their cumulative weights have dropped, from an average of 242 pounds in 2012 to 237 last season.

The game has changed. The Carolina Panthers are lauded for having one of the best linebacker corps in the NFL. Luke Kuechly (238 pounds), Thomas Davis (235) and Shaq Thompson (230) are all on the lighter side.

A few of those players might not be built for the primary purpose of bowling over fullbacks and dropping a running back in the backfield, but they can match up in coverage, defend the flats and go sideline to sideline.

Besides, outside of the Saints, how many teams even roster a fullback anymore? Not many.

“We took Kwon (Alexander) last year,” Tampa Bay general manager Jason Licht said of the former LSU standout. “Although we took him in the fourth round, we feel like he’s a first-round type of player. He’s an undersized guy (at 6-1, 227 pounds), but it’s more about their physicality and their ability to make tackles and their ability to run and play good football than it is size.”

Small is the new normal. When considering those numbers, Jones still seems a little light, but he’s only a few burgers away from average size, and he doesn’t need to be as big as the guy lining up in the middle since he’ll play on the weak side in the NFL.

Similarly, the uproar about Notre Dame’s Jaylon Smith weighing in at 229 pounds was overblown. He should bulk up once he’s done rehabilitating his surgically repaired knee, though there are now major questions about his value since it has been revealed that he might have nerve damage in his leg.

“Linebackers are changing. They’re getting smaller,” said Ohio State linebacker Darron Lee, who measured in at 6-1 and 232 pounds. “The game’s getting faster, and you need guys that can cover. ... Quarterbacks are getting the ball out faster; they’re targeting linebackers. That’s what I see on Sundays.”

The Saints saw it last year, and the Washington Redskins saw the Saints’ vulnerability.

After watching New Orleans get picked apart little by little on underneath routes and in the flats week after week, Washington quarterback Kirk Cousins elected to throw to these areas almost exclusively during a 47-14 win last season.

These routes were a silent killer for the Saints last season. According to The Advocate’s charting, teams picked up 1,035 yards on 111-of-138 passing on short throws near the sidelines.

New Orleans attempted to protect against this outcome last offseason by acquiring weakside linebacker Dannell Ellerbe in a trade that sent Kenny Stills to the Miami Dolphins, but he battled a hip injury throughout the season and was limited to six games.

Ellerbe has since agreed to restructure his contract, which makes him more affordable, but his injury history — he has played in seven games the past two seasons, and never all 16 — has to create some concerns about his availability and ability to help the Saints defend those areas of the field.

For that reason, a coverage linebacker could be one of New Orleans’ top needs this offseason.

Smith looked like a solid fit since he can play all three linebacker positions, but concerns over his health could take him off the board. The other top coverage linebacker, UCLA’s Myles Jack, could be gone before the Saints pick at No. 12. That could put someone like Jones or Lee on the Saints’ radar in the second round.

If that happens, people will look at the players’ weights and wonder whether either is big enough to thrive and survive in the NFL. The critics will say they need to bulk up and add weight.

After doing that, they’ll raise concerns about the players maintaining their speed and agility with the added weight and mass.

What they won’t realize is that light is the new normal, and neither of those players is much different from the rest of the linebackers patrolling NFL fields.