Despite coming from a small-college program (Samford) and having a limited football background, Tartt has wasted no time as a rookie making an impact at strong safety after Pro Bowl starter Antoine Bethea went on injured reserve. Tartt has notched 33 tackles, two interceptions and a forced fumble in the past five games while also establishing himself as an effective blitzer in coordinator Eric Mangini’s defense.
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New England cornerback Logan Ryan
Ryan’s skills were on full display in last Sunday’s 30-24 loss to Denver when he helped limit Broncos wide receiver Demaryius Thomas to just one catch on 13 targets. Ryan, who entered the starting lineup in Week 3 after Tarell Brown suffered a season-ending foot injury, is tied for sixth in the NFL in interceptions with four. Ryan also has a team-high 16 passes defensed and ranks third in tackles with 54.
Detroit linebacker Josh Bynes
Replacing one of the NFL’s top weak-side linebackers and a team leader like DeAndre Levy isn’t an easy task. Bynes has done an admirable job with Levy missing almost the entire season with a hip problem that has landed him on injured reserve. Bynes ranks second on the Lions in tackles with 58.
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Dallas running back Darren McFadden
McFadden was originally supposed to serve as a complementary piece in a running back trio that also featured starter Joseph Randle and fellow backup Lance Dunbar. McFadden is now essentially a committee of one after Randle was released because of off-field problems and Dunbar suffered a season-ending knee injury in Week 4 against New Orleans. McFadden, whose previous seven seasons with Oakland were largely marred by injury, has done his part with three 100-yard rushing performances in the past six games.
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Minnesota center Joe Berger
The loss of standout John Sullivan to a season-ending back injury hasn’t proven devastating thanks to the Vikings wisely re-signing the versatile Berger during the offseason. The 33-year-old Berger is part of an offensive line that has paved the way for Adrian Peterson to post a league-high 1,164 rushing yards, helping to lift Minnesota (8-3) into sole possession of first place in the NFC North.
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San Francisco quarterback Blaine Gabbert
Although he has yet to prove himself as the franchise passer Jacksonville hoped when making him the No. 10 overall pick in the 2011 draft, Gabbert has played the best football of his four-year NFL career after replacing the ineffective Colin Kaepernick in Week 9. Gabbert has completed 65.3 percent of his passes with four touchdowns and three interceptions while posting a 1-2 record. In comparison, Kaepernick’s completion percentage was 59.0 with six scores and five INTs as the 49ers opened 2-6. Gabbert, whose contract expires at season’s end, has the chance to bolster his free-agent stock over the final five games with Kaepernick now on injured reserve following shoulder surgery.
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Arizona running back Chris Johnson
Johnson went from being unsigned to joining the Cardinals as a backup in training camp to starter once Andre Ellington was injured in the Week 1 win over New Orleans. Johnson, who trained at FOX Sports NFL Insider Jay Glazer’s Unbreakable gym in Los Angeles during the offseason while recovering from a gunshot wound, is a strong candidate for NFL Comeback Player of the Year honors. After a dip in production last year with the New York Jets, Johnson is on pace for his seventh career 1,000-yard campaign in his eight-year NFL career. He currently ranks fourth in the league rushing rankings with 814 yards. Johnson suffered a leg injury in last Sunday’s 19-13 win over the 49ers, which would lead to more opportunities for rookie David Johnson.
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Kansas City running back Charcandrick West
There was little reason for hope with Kansas City sitting at 1-4 when Chiefs star running back Jamaal Charles suffered a season-ending knee injury. West has provided plenty, helping Kansas City rebound with a five-game winning streak in place of his close friend and mentor. An undrafted second-year player from Abeline Christian, West has proven capable as a rusher and receiver out of the backfield in the same fashion as Charles. After he missed last Sunday’s 30-22 win over Buffalo with a hamstring injury, the Chiefs hope to have West back for this Sunday’s key AFC West matchup at Oakland.
Getty ImagesAlan Crowhurst
Seattle running back Thomas Rawls
The Seahawks are so reliant on their running game that the season-long injury issues being experienced by Marshawn Lynch could have torpedoed Seattle’s hopes of making a third straight Super Bowl appearance. However, the club is still squarely in the playoff hunt thanks to the surprising emergence of Rawls, an undrafted rookie free agent from Central Michigan. Recently compared to Pro Football Hall of Fame running back Earl Campbell by Seahawks coach Pete Carroll, the rugged Rawls has rushed for 685 yards with a gaudy 5.6-yard average.
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Indianapolis quarterback Matt Hasselbeck
There’s no question that Andrew Luck will be the Colts’ franchise quarterback for years to come. Hasselbeck, though, has proven his best days aren’t in the past when replacing an injured Luck during two separate stretches. The 40-year-old Hasselbeck is 4-0 as a starter, having completed 64.7 percent of his passes with seven touchdowns and two interceptions. Hasselbeck has added a spark to the offense with his prudent decision-making and quick throws in the passing game to take some of the heat off a struggling offensive line.
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Pittsburgh running back DeAngelo Williams
After being exposed in last season’s playoffs, the Steelers were determined not to get caught short-handed if Le’Veon Bell got injured again. Williams, who was signed to a two-year, $4 million contract during the offseason after nine years in Carolina, has proven one of the NFL’s top bargain-basement acquisitions. With almost 800 yards rushing and receiving, the 32-year-old Williams picked up the slack when Bell served a two-game drug suspension to open the season and again when Bell landed on injured reserve after hurting his knee against Cincinnati in Week 8.
Denver quarterback Brock Osweiler
What was once thinkable now looks like it will become reality: A healthy Peyton Manning ending this season sitting on the bench. With two straight victories as a starter -- including last Sunday’s 30-24 overtime win over New England that knocked the Patriots from the unbeaten ranks -- Osweiler is now expected to keep the first-team job even when Manning recovers from his foot ailment.