Slot corners not only need to deal with running backs and tight ends from his base position; they also must cover the NFL's best receivers.

As a direct response to the NFL's shift towards more shotgun formations, more dynamic passing games and schemes with more receivers, defensive coaches have switched their thought process. The nickel defense, which used to be thought of as an important sub-package, has become the base defense for most teams. Linebackers have to patrol more of the field, because there's generally fewer of them, and slot cornerbacks are now de facto starters. That's a big shift from a decade ago, when nickel cornerbacks were the guys who were too small or slow to deal with top receivers. Now, that slot man not only needs to deal with running backs and tight ends from his base position; he also must cover the NFL's best.

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Last season, per Pro Football Focus, Randall Cobb was the league's most prolific slot receiver, with 75 catches for 1,067 yards and 12 touchdowns inside the numbers for the Packers. Cobb had already been established as that kind of receiver. The second-best slot man was Eagles rookie Jordan Matthews, who was drafted by Chip Kelly with the express purpose of working the middle. The third-most productive slot receiver last season was Dolphins rookie Jarvis Landry, who was also selected for that purpose—at least, to a large extent. More surprisingly, the guys who used to make their living on the outside—receivers like Reggie Wayne, Anquan Boldin and Larry Fitzgerald—are spending more and more time in the slot. That's not just a factor of age; it's just as much about matchups.

The old-school slot cornerback was asked to do little more than hand off his man in zone coverages. Now, he must adapt to option routes, take speed receivers all the way up the seam and read more complex route concepts on the fly. Guessing wrong is not an option.

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“There's been so much passing game in the last 10 years, and I think the nickel, it's half the game,” Pete Carroll told me last year. “Half the game, you're in nickel or some kind of substitution defense. So, it's whichever way you want to look at it; maybe that's base and the other part is substitution now. We're divided about 500 plays to 500 plays year in and year out, and it's a big deal. That's why [on defense], we have more than 11 starters. We've got 15-16 starters that we see, and you can tell, depending on the opponent and the situation in the game, how many of those guys we'll move in and out, and feel comfortable doing that.”

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According to data shared with SI.com by Steve Palazzolo of Pro Football Focus, Seattle played with five or more cornerbacks on the field for 59 percent of their defensive plays in 2014. Everyone saw how Carroll's coverages were negatively affected by the injury to slot cornerback Jeremy Lane in Super Bowl XLIX. Seattle's 59 percent was just below the league average of 60 percent. That's right: NFL defenses took at least one linebacker off the field and replaced him with a defensive back on six of 10 plays in 2014. That's up from 40 percent in 2011, 44 percent in 2012 and 49 percent in 2013, according to Football Outsiders data. The Lions led the NFL with five or more defensive backs on the field 76.3 percent of the time in 2014, deploying four defensive backs on just 20.5 percent of plays.

Denver's Chris Harris is probably the most prominent slot cornerback in the league. He's been great at it for a number of years, and he's moved outside in a more traditional role recently. The Broncos signed him to a five-year, $42.5 million contract extension last December, and we've covered just how adept he is in that role before, so it's safe to say the cat's out of the bag with Mr. Harris. Last season, Harris was once again marvelous in the slot, allowing 20 receptions on 32 targets for 143 yards, no touchdowns, one interception and a 59.8 opposing quarterback rating. Who else has developed a niche in this ever-growing role? Here are the league's best slot cornerbacks, and what makes them special.

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Jerraud Powers, Cardinals

Selected by the Colts in the third round of the 2009 draft out of Auburn, Powers was primarily an outside cornerback during his first five years in the league, but last season, Cardinals defensive coordinator Todd Bowles deployed him as a multi-positional weapon to great effect. In 2014, Powers led the NFL in slot targets with 75, and he allowed 47 catches for 548 yards—but only one touchdown, with three interceptions and a miniscule 72.5 opponent passer rating. On his way out to his new position as the Jets' head coach, Bowles praised Powers's versatility and implied that it was time for him to play a bigger role.

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“It’s going to be tough beating Powers out,” Bowles said in March at the NFL annual meeting. “Powers is tough. You keep forgetting about Powers. Powers is one of the best guys back there. He doesn’t get the credit. It’s going to be tough beating Powers out... [he] can play wherever you need him: corner, safety, nickel. Don’t underestimate him, please. He’s a tough guy.”

Well, we're not underestimating him here. Here's Powers picking off Kirk Cousins in a Week 6 contest against the Redskins. There's 4:13 left in the game, and Powers is lined up over receiver Andre Roberts in the middle of a trips right formation with tight end Jordan Reed inside and receiver DeSean Jackson outside. Watch how Powers reads the play and jumps the route. Slot cornerbacks often have to read multiple receivers at once because they're not “island” players—they don't have isolated matchups against receivers as often as outside cornerbacks. Powers understands that, and it pays off here.

“I’m thinking screen,” Powers told the team's official site. “Kirk Cousins is probably thinking we’re bringing a lot of pressure when we’re not. We were faking a blitz. Whenever you think a blitz is coming, the easiest way to get out of it is throwing a quick screen. Right now, me and Pat [Peterson] are thinking screen because DeSean is not lined up all the way in the bunch. He had space so he would have room to catch the screen.”

Here, against the Lions in Week 11, Powers lines up over Golden Tate in the left slot, only to read Matthew Stafford's throw to Calvin Johnson. He checks Tate off to linebacker Larry Foote, and doubles down on Megatron, who's originally covered by Patrick Peterson. He may have missed out on a touchdown by failing to reel in an interception, but Powers had this one read all the way.

Bowles may be right that Powers is ready to be a starter outside opposite Peterson, but new defensive coordinator James Bettcher would do well to put Powers in situations where his versatility can be featured. It's become an important part of Arizona's defense.

Brandon Boykin, Eagles

Many Eagles fans wondered why, with their outside cornerback duo of Cary Williams and Bradley Fletcher getting toasted on an alarmingly regular basis, Chip Kelly didn't direct defensive coordinator Billy Davis to put Brandon Boykin out there as a "starter" more often. After all, when he was an outside corner in 2014, Boykin was more effective than either Williams or Fletcher—not that he had to clear a very high bar. But to ask the question is, perhaps, to misunderstand the definition of a starting cornerback in today's NFL. Boykin was a starter: He played 150 snaps outside and 374 snaps in the slot, allowing no touchdowns on all his targets. Williams and Fletcher allowed a combined 14 touchdowns. It could easily be argued that Boykin was the team's most valuable defensive back, which the Eagles seem to have confirmed by the fact that he's the only one of the three still on the team's roster.

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“It really is how we practice [that determines where you play], and he practices as our nickel corner,” Kelly said last September of Boykin. “It's a very vital position for us. Billy said that that's a starting position for us, I say that's a starting position for us, that's kind of where it is.”

At 5'10" and 185 pounds, Boykin doesn't fit Kelly's prototype of a starting outside cornerback, but that's less relevant in the grand scheme of things, because Boykin—like all the best slot corners—provides more value from more spaces.

Here, with 2:09 left in Philly's Week 12 game against the Titans, Boykin gives rookie quarterback Zach Mettenberger a lesson in disguised coverage. Boykin starts in the slot but switches coverage with Nolan Carroll and jumps the route just in time to pick off the pass intended for Justin Hunter.

In Week 16 against the Redskins, Boykin reacts to tight end Jordan Reed going in motion away from him by guessing that Reed might move back over to his side on a crossing route. Boykin guesses right, and although Reed catches the pass, he doesn't do much after that.

Casey Hayward, Packers

Through his first three years with the Packers, Hayward was primarily a slot man in Dom Capers's defense, which asks its cornerbacks and safeties to move around pretty frequently. But with the loss of Tramon Williams and Davon House in free agency, it's expected that the Vanderbilt alum will see more time on the outside in 2015. He's done so very well as an injury replacement at times, and secondary coach Joe Whitt believes that Hayward is ready for whatever challenge he's given.

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“Casey has played better than most people realize, and he deserves more reps than he has played,”​ the coach said in 2014. “I'm pleased that he hasn't complained or done anything like that because he grades out so high every week, and I want to give him more snaps, but there's only so many to go around.”

Hayward has made it clear that he wants to start outside more often—after all, that's where the money is, and he's in the final year of his rookie deal—but he's been highly valuable in the slot. Last season, he allowed just 16 catches on 25 targets for 168 yards, two touchdowns and three interceptions from the slot, and the tape shows a player with a solid understanding of the slot requirements. Inside cornerbacks must be able to adjust to multiple route concepts and single-receiver option routes. Watch how he stays in the middle of the Dolphins' routes in this Week 6 game, coming away with the interception.

And in the regular-season finale against the Lions, Hayward starts off covering Calvin Johnson in the slot, but breaks off to cover Reggie Bush, stopping Bush from reaching the first down marker. The ability to cover this much horizontal space in a hurry is one sign that you're looking at a great slot cornerback.

“I'm just going to keep doing what I do,” Hayward told ESPN's Rob Demovsky. “My numbers don't lie about how I've played. I just keeping playing ball, keep doing what I do when my opportunities come, just keep knocking on that door. The coaches know what I can do. I'm in a great situation. I came into a great situation. I was led by some veterans when I first got here. Those guys helped me and showed me the ropes.”

If Hayward provides high value on the outside, that won't be a surprise. And the Packers have another slot man with a lot of potential in third-year man Micah Hyde.

Brice McCain, Dolphins

In 2014, the Dolphins' secondary may have cost them a spot in the playoffs. Cornerback Brent Grimes struggled at times, and bookend Cortland Finnegan's play indicated that it might be time for him to hang 'em up—which he did after the season ended. The Dolphins are still trying to figure out what they'll do opposite Grimes, but one move they made could pay unexpected dividends. Signing free agent cornerback Brice McCain to play the slot was a relatively unheralded but very smart move by general manager Dennis Hickey.

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McCain comes to the Dolphins with a two-year, $5.5 million contract, and he earned that with the Steelers last season. In the slot, he was targeted 35 times, giving up 22 catches for 235 yards, no touchdowns, one interception and a 70.5 opposing quarterback rating, which tied with Hayward for the league's second best behind Chris Harris. McCain had been an outside cornerback for the Texans before and was exposed mightily in that role, but something about Pittsburgh's defense and his role in it really worked.

McCain's interception came in Week 5 against the Jaguars, when he lined up in the slot over Allen Hurns, with Cortez Allen covering on the outside. At the snap, McCain read the crossing routes run by Hurns and Mike Brown and took the pick to the house.

“The thing that I did like about Brice is he capitalized on the opportunity,” coach Mike Tomlin said after the game. “It’s the type of week he had in practice. He probably had four picks this week in practice. It just reinforces the concept that the things you do in practice have an opportunity to show up in the game. He had a good week in practice and it was just good football justice to see him have an opportunity like that and cash in on it.”

Another example of “good football justice”: Steve Smith's two-yard reception against McCain in Week 9 against the Ravens. McCain handed Torrey Smith off to the zone at the snap, then put lockdown coverage on Smith. The coverage was so close, and so effective, that you can see Joe Flacco adjust to it before he throws.

Is it time to re-think the importance and value of the slot cornerback? It may very well be. These players are starters, they're crucial to the success of their defenses, and based on current trends, they'll only become more important in time.