There are a lot of bad football clichés, but the worst might be “next man up.” The phrase carries an obvious lack of humanity (gee, what happened to the last man up?), and it’s also mindlessly ubiquitous, popping up after seemingly every injury.

The Falcons said it this week about replacing Tevin Coleman and last week about repopulating their depleted linebacker corps. Steelers coach Mike Tomlin says it so much that it’s become a team philosophy: “Guys take pride when they’re the next man up,” linebacker Jarvis Jones said this month. When the Seahawks lost tight end Luke Willson for a few weeks this month and Nick Vannett replaced him, offensive coordinator Darrell Bevell wanted everyone to know: “It really is the next man up.”

This flippant phrase indicates that all injuries are created equal. But they aren’t, and neither are the players they force into action. Sometimes there’s no replacing the player who got hurt. Sometimes the next man up sucks.

Curiously, despite the level of discussion they inspire, injuries remain the X factor we know the least about. Broadly speaking, we know that they can sink a season. When it comes to specifics, however, teams and the public know more about how jersey color impacts performance than how specific injuries hamper success.

But in 2015, a group of researchers from the University of Missouri and Southern Utah University sought to change that, releasing a paper in the Journal of Sports Economics called “Positional WAR in the National Football League.” Their goal: to identify the value of each position by assessing what happens when the best player at each spot on the depth chart falls.

“We wanted to know: What happens when all of the sudden a team unexpectedly loses a player?” said Joshua Price, assistant professor of economics and finance at Southern Utah. “How is a team affected by losing that starter?”

To determine that, they studied three NFL seasons’ worth of data, alternating years from 2008 to 2012. They calculated the injury data per game, but presented the variance over four-game sets to account for abnormalities or multiple starters at certain positions. They compared teams’ records during injury absences to what preseason oddsmakers believed teams should have managed, adjusted for a four-game window.

The most important position was not a shock: The researchers found that if a team loses its starting quarterback over four games, it will, on average, manage 1.3 fewer wins in that span. (Say, didn’t the Patriots drop a game without Tom Brady in the first four weeks?)

They also found that wide receivers, tight ends, and exterior offensive linemen were all on the second tier of importance, with each starter costing his team about half a win over a four-game absence. Then there was a surprise: “There was a tie for last place,” where injuries caused noticeably less harm to a team, Price said. The first spot was running back, which has been borne out anecdotally this season: Look at how the Vikings and Bucs are performing without Adrian Peterson and Doug Martin, respectively. The next was interior offensive linemen. And then, incredibly, “every defensive position,” Price said. “That surprised us.”

Over four games, an injury to a starting linebacker docks a team .079 wins, while a cornerback injury costs .002. The study found that teams can overcome the vast majority of defensive injuries, but not offensive ones. We’ve always known that quarterback injuries are murder, but we held that thought for stars on defense, too. No one would believe, for instance, that the Lions would be A-OK despite a stack of defensive injuries. But they are.

Of course, there will always be exceptions to this or any other finding: Right now, Tony Romo’s injury looks more like a blessing in disguise than a season killer for the Cowboys. Trent Green was supposed to be the man for the 1999 Rams, and when he got hurt, Kurt Warner famously took that team to the Super Bowl. But those are the exceptions. More common: the struggles the Browns and Bears are experiencing this season, or the misery the Colts faced without Andrew Luck last year.

Price theorized in an interview that this mostly has to do with adaptability: If a team loses a starting cornerback, it can compensate by playing more zone. It can add more safety help. It can generally change its entire scheme. If a team loses a pass rusher, it can drop more cornerbacks to swamp wideouts. Defenses can hide their problems easier with scheme.

This study shows that all injuries are not created equal when it comes to their impact on wins and losses. Armed with this research plus film study from 2016, we can identify the five injuries that are defining this NFL season.

The Vikings’ Tackles

The paper estimated that an injury to a starting outside offensive lineman costs a team about half a win every four games. On Sunday, the Vikings were missing two outside offensive linemen, and that probability revealed itself quite loudly.

Matt Kalil went on injured reserve with a hip injury after Week 2 and Andre Smith was placed on injured reserve two weeks ago with an arm injury. Neither is expected back this season. When healthy, Kalil was criticized for his poor play, but the Vikings desperately needed even his level of competence on Sunday. The team has done a remarkable job of overcoming nearly everything else, barely missing a beat despite losing Peterson and starting quarterback Teddy Bridgewater and being without defensive tackle Sharrif Floyd since Week 1. But the Vikings avoided suffering from Bridgewater’s injury by acquiring another team’s starter instead of relying on a backup, inserting Sam Bradford by Week 2 and getting off to a 5–0 start.

Without both starting offensive tackles, however, things fell apart against the Eagles. The team moved T.J. Clemmings and Jeremiah Sirles to the tackle positions, and rotated in overmatched veteran Jake Long against the Eagles. Let’s see how that went:

Imagine the phrase “another strip sack” being an accurate representation of your play.

Bradford threw his first interception as a Viking in this game, and it wasn’t his fault:

Here’s another angle of the line on that interception:

Wow. There are rumors that Cleveland’s Joe Thomas and San Francisco’s Joe Staley are available via trade. Minnesota already sold the farm for Bradford, but they should do whatever they can to get one of these players, because they would provide a massive boost to the Vikings’ Super Bowl hopes. They might need both.

Steelers QB Ben Roethlisberger

Ron Jaworski relayed in his book The Games That Changed the Game that he once asked then-Colts offensive coordinator Tom Moore why Peyton Manning got all of the snaps during a practice instead of some going to a backup. Moore answered: “Fellas, if ‘18’ goes down, we’re f***ed. And we don’t practice f***ed.”

Well, the Steelers don’t practice f***ed, either. Roethlisberger’s torn meniscus could reportedly keep him out for more than a month, which would make this the second straight season that he’d miss that much time. What makes this such a blow to the Steelers is that we are actually in an era of good quarterback health (Romo notwithstanding): 17 NFL quarterbacks started 16 games last season, the second most since the NFL started its current 16-game, 17-week scheduling format in 1990.

The paper estimated that a month off for a quarterback results in a 1.3-win drop for a team. The Steelers went 2–2 last season when a backup — Landry Jones or Michael Vick — started. They are already 0–1 this season with Roethlisberger out and Jones in. That dip is a nightmare in a league where home-field advantage has gotten increasingly important, with the home team winning the past six combined conference title games in the AFC and NFC.

The Steelers can’t work toward an elite record with Roethlisberger out, as we saw this week with the inexperienced Jones under center and a loss to the Patriots on the board. If Daniel Day-Lewis dropped out of a project at the last minute and got replaced by Kevin James, there would presumably be some tweaks to the production. But at points on Sunday, the Steelers’ play calling made it seem like they thought Roethlisberger was still out there. Jones made some fairly risky throws on Sunday, and while they’re ones Roethlisberger routinely nails, they’re not exactly Jones’s forte. There’s a reason James wasn’t considered for Lincoln:

Bills WR Sammy Watkins

Last season, Tyrod Taylor ranked fifth in the NFL in yards per pass completion and yards per attempt. If you married the Bills’ solid passing game from last season with their elite, Shady McCoy–led rushing attack from this season, you’d be looking at a real contender. But offseason foot troubles followed Watkins into the season, and he was placed on injured reserve after Week 3.

The difference in the offense has been startling. Taylor is averaging more than a yard less per throw this year than last, which makes sense considering that Watkins led the league (among players who started at least three games) with 10.91 yards per target in 2015. He was in a rarefied group of players able to consistently get open deep, and Taylor was able to find him. Without Watkins the offense is relying more on McCoy, who is now battling a recurring hamstring injury. Taylor is trying to develop a new deep threat in Marquise Goodwin, who has three touchdowns this year, including a 67-yarder on Sunday. But Goodwin isn’t Watkins: He’s catching only 37 percent of the passes thrown his way, an embarrassingly low percentage, especially compared to Watkins’s 62.5 percent mark from last year.

Having a reliable deep threat would change this offense dramatically. Hell, in a weak AFC, an offense that can run the ball and throw deep would make the Bills playoff favorites. Without Watkins, that won’t be the case this year.

Jets WR Eric Decker

History will remember Ryan Fitzpatrick’s 2015 season fondly, but not enough of us will remember that as the year Eric Decker saved Fitzpatrick. Decker and Brandon Marshall created the best one-two receiving punch in the league last year, making Fitzpatrick look like a quarterback worthy of the offseason contract drama he wound up putting the Jets through.

The sequel hasn’t gone as planned. A shoulder injury limited Decker early, and he was shut down after just three games. This Decker-less reality is Fitzpatrick’s own worst nightmare. Decker was among the best red zone receivers in the league last season, targeted inside the 20-yard line 36.8 percent of the time, more than any other player. He also led in target percentage inside the 10-yard line, a stat usually associated with tight ends (Kyle Rudolph and Gary Barnidge were nos. 2–3).

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Too many people have chalked up Fitzpatrick’s regression to Fitzpatrick being Fitzpatrick, but don’t discount the impact of Decker’s injury. A team improves when field goals become touchdowns, but for the Decker-less Fitzpatrick, touchdowns have become interceptions and the offense has become stale. The team’s secondary targets aren’t able to replicate Decker’s production, and the drop-off in talent is so stark that Decker’s absence might actually get somebody hurt.

Chiefs LB Justin Houston

Two high-profile defensive injuries support the paper’s finding that injuries on that side of the ball don’t heavily impact record. The first is J.J. Watt, whose Texans are 4–3, and the other is Justin Houston, whose Chiefs are 4–2. But Houston’s absence is worth noting, because it’s changing the way the Chiefs play. And if Houston can’t return to the field soon, that could catch up to them.

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Last season, Houston totaled 7.5 sacks through 11 games, allowing the Chiefs to be more aggressive because they knew he could get after the quarterback on basically any play. They were fourth in sacks, with 47. This year they have a total of eight, tying them for last in the league. That’s a massive dip. In contrast, the Texans were tied for third in the league last year in sack percentage, at 7.5 percent. Even without Watt, they’re ninth this year, at 7.4 percent.

Kansas City’s pressure scheme is, uh, a little different without Houston:

Somehow, the Chiefs won that game. Houston’s injury isn’t yet leading to losses, but it’s sure making Kansas City look bad.