There isn’t a scarier moment in football.

The star of the team lies face down on the turf, writhing in agony. The play continues past him and almost no one seems to have noticed that only 21 men are running down the field.

For those watching on TV, at the end of the play the camera will cut to a shot of the star clutching his knee as trainers rush on the field. These are the plays that make or break a season, and possibly the job of a coach. The backup hurriedly warms up on the sideline as the announcers wonder how the team can possibly recover its Super Bowl hopes without the star.

As the player heads to the locker room, fans everywhere wonder who will take over while the game hangs in balance.
Obviously some teams are better prepared for injuries than others. When Carson Palmer went down last year the Bengals had to call on Ryan Fitzpatrick, while the Patriots were able to move Matt Cassel into the starting role when Tom Brady was lost for the year. Players like Cassel seem to surface every year, just waiting for an opportunity to perform.

A quick look at the top skill players in the league will reveal more than a few players that are now perennial All-Pros, who once had to fight their way on the field.

But knowing who these players are doesn’t just help NFL coaches and GMs; rather it can help you find gold on your league’s waiver wire.

Everyone knows Darren Sproles is a talented backup and LaDanian Tomlinson owners will likely find a spot on their bench for the diminutive Chargers running back. But who else is just a play away from stardom?

1. Darren Sproles, Chargers
The pint-sized running back played much better than anticipated after LaDanian Tomlinson was injured last season. Sproles scored three times in two playoff games and averaged 5.4 yards per carry in 2008. He got the franchise tag this year and the team did consider releasing Tomlinson, so he’ll get his touches.

2. Chester Taylor, Vikings
Because Adrian Peterson has been taken out in passing downs, Taylor gets plenty of opportunities. He gained 798 total yards and scored six touchdowns last year. Since Taylor’s rookie year, he has not gained less than four yards a carry. If Peterson continues to be unable to pass block, Taylor will have a real chance to contribute in his contract season.

3. Steve Breaston, Cardinals
This is somewhat of a cheat, since Breaston is the third wide receiver and a proven commodity. But we’ll run with this as long as Larry Fitzgerald and Anquan Boldin are in the desert. Breaston had more than 1,000 receiving yards last season, and it’s probably not reasonable to think of him doing that again, but if he can grab a few more touchdowns than last year, when he had three, Breaston will be a valuable fantasy player.

4. Chris Wells, Cardinals
One of three Cardinals to make this list, its possible Wells will own the starting job by the time training camp breaks in the desert. The Ohio State product is a punishing running back and will see red zone opportunities regardless. In college, Wells had some trouble staying healthy, but if he can find a way to stay on the field, this is the rookie to watch out for.

5. Felix Jones, Cowboys
Jones was injured in his rookie season, but he showed immense promise before going down. The Arkansas product averaged 8.9 yards a carry in six games. The problem for Jones will be getting carries in an offense that includes Marion Barber and Tashard Choice.

6. Fred Jackson, Bills
Marshawn Lynch’s three-game suspension will provide Jackson with an opportunity to force Buffalo to give him carries all year. In Jackson’s lone start last year, he rushed for 136 yards against a good Patriots defense. He can also catch the ball, piling up 317 yards last year.

7. LeSean McCoy, Eagles
No one is really sure how Brian Westbrook’s offseason surgery will impact the longtime Philadelphia running back, but he is 30 years old. McCoy is in a great spot to have impact with Westbrook missing the entire preseason.

8. Donald Brown, Colts
It seems that Indianapolis doesn’t believe in Joseph Addai, which makes Brown an interesting backup. The first-round pick out of Connecticut, Brown could be this year’s rookie running back to watch. Right now though, Brown is not a short-yardage back, so touchdowns will probably not be coming his way.

9. Jeremy Maclin, Eagles
DeSean Jackson’s success last season is an indicator that talented rookie wide receivers are a great fit with the Philadelphia offense. Maclin didn’t play in a pro style offense at Missouri, but he’s blazing fast with great hands and better size than Jackson. Donovan McNabb will find him and he will score touchdowns.

10. Shonn Greene, Jets
Greene is another big, Big Ten running back. Combine his 235-pound frame with a 31-year old Thomas Jones; Greene is in an outstanding spot to score touchdowns. If Jones goes down, the Jets seem to have a lot of faith in their rookie out of Iowa; they did trade up to draft him after all.

11. Austin Collie/Pierre Garcon, Colts
Whoever wins the third wide receiver spot in the high-octane Colts’ offense will become fantasy relevant. Neither one was picked high in the draft nor are they burners. But they are solid possession receivers with great hands. As long as Peyton Manning is throwing them the ball, they’ll be just fine.

12. Matt Leinart, Cardinals
Kurt Warner is a fragile, old quarterback. Leinart is worked out with Tom Brady in the off season and seems to have taken last year’s demotion to heart. Were Warner to go down or be ineffective, Leinart could finally become the type of pro expected of the Heisman winner.

13. Rashard Mendenhall, Steelers
A first-round draft choice last year, Mendenhall struggled through preseason and then was injured four games into the season. But Willie Parker is incapable of being an every down back, so Mendenhall has a great chance to be the short-yardage guy. Look for touchdowns out of another large Big Ten running back.

14. Chris Simms, Broncos
This assumes Kyle Orton is the starting quarterback in Denver. Simms has proven himself as a starter before and Orton has proven to be average. It’s possible Orton flourishes with Josh McDaniel’s’ offense and all the weapons in the Mile High city, but it’s also possible Simms has his first shot at being a starter since that vicious hit ruptured his spleen.

15. Kevin O’Connell, Patriots
After Matt Cassell’s and Tom Brady’s unbelievable success, O’Connell just has to be on this list. There is nothing to say that Brady isn’t fully recovered or will be injured again, but with this offensive system unknown quarterbacks can have plenty of success. He was only 4-of-6 last year, but as the Patriots’ backup he is worth knowing.