The list of key players injured this season would make even some coaches shudder. Particularly when they see who has to fill in.
A look at just the running backs who have been sidelined in 2015 is foreboding: Jamaal Charles, Le'Veon Bell, Justin Forsett, Arian Foster, Chris Johnson, Mark Ingram, Carlos Hyde, Reggie Bush.
Does anyone from Dallas to Baltimore to Indianapolis need to be reminded of the quarterbacks who have gone down?
Of the nearly 50 linebackers out, replacing the likes of Terrell Suggs, DeAndre Levy, Alex Ogletree and Jon Beason is a difficult chore.
So when coaches, personnel directors, owners - even players - speak about depth, listen deeply. It's become critical.
''The guys come in and they go,'' Chiefs coach Andy Reid says. ''If you practice, you practice. If you can't, you can't, and we roll. That's the approach we've taken and the guys are good with it.
''They battle like crazy to get themselves back and if they can't make it, they have trust in the guys around them that they'll step in and do a good job. We've kind of just left it at that.''
Certain teams have been so ravaged by injuries from the outset of the schedule - Baltimore, San Diego, Dallas - that their seasons basically were over by Halloween. They were damaged as much by losing stars (Suggs, Tony Romo, Keenan Allen) who almost never can be adequately replaced, as they were by having inept backups at other positions.
Others who started strongly are feeling the sting of key injuries now: certainly Cincinnati without Andy Dalton and with Tyler Eifert in the concussion protocol; Denver as Peyton Manning finally returns to practice; Seattle with first Marshawn Lynch and then his replacement, rookie standout Thomas Rawls going down; and New England (Edelman, Gronkowski, Hightower, Blount).
But injuries don't have to define a season. While the next man up theory always is applied by players and coaches when a starter gets hurt, it rarely works. A second-stringer is such because he isn't as good as the regular guy.
But he can sometimes do just enough. Some backups will emerge as quality players, if not stars. For the strongest teams, that's also enough.
Charcandrick West and Spencer Ware in Kansas City are solid examples. When do-everything RB Charles tore up his knee in Week 5 against Chicago, the Chiefs dropped to 1-4. Gloom and doom clouded the KC skies.
The Chiefs now are 8-5, thanks mostly to a dynamic defense and mistake-free quarterbacking by Alex Smith. But the work of the two replacement running backs has played a significant role.
In turn, they say the tutoring of Charles helped them make quick contributions.
''I'm happy for their success,'' Charles said. ''I knew if we got on the same page, we'd be winning. I feel like they're all clicking on the same page.''
Other backups who have come to the forefront this season range from Lions RB Theo Riddick to Panthers safety Kurt Coleman to Saints WR Willie Snead to a slew of Patriots offensive linemen.
Even Ryan Fitzpatrick. The 11th-year quarterback came to the Jets as a veteran presence behind Geno Smith, and was thrust into the starting role when Smith was punched out by a teammate in preseason and suffered a broken jaw. Fitzpatrick has been everything (and more) that Brandon Weeden, Matt Cassel and Matt Schaub have not in 2015.
''He is what we expected him to be in terms of his strengths, not only as a player, but from an intangible standpoint,'' said Jets general manager Mike Maccagnan, who was in Houston's front office last year while Fitzpatrick was on the Texans.
''I think I've just gotten better every year,'' Fitzpatrick said. ''I think I've learned a lot more about the game, about myself. Just try to continue to improve each year and then just the way that it's all come together with the system that I've been familiar with and guys in this offense that are great playmakers, that make my job easy.''
Joining the starting lineup is never easy for a backup, though. He doesn't get enough repetitions during practice. He isn't a major part of a game plan.
But, yes, he is the next man up.
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AP Sports Writers Dennis Waszak Jr., and Dave Skretta contributed to this story.
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