One of the great things about the increase in exposure and analysis of the NFL going on right now is that we get to witness the level of debate rise in real time.

Evaluating how good players were used to be confined to a few basic raw statistics, highlight reels and how many talking heads happened to agree with your stance, but now we see something completely different.

Take analyzing cornerback play as an example. It isn’t enough for some people to simply dominate your man or your side of the field in coverage – the way Richard Sherman has done for the past few seasons – they want you to track an opponent’s top receiver and demonstrate you can do it every down in the toughest situations. To some, the fact that Sherman doesn’t track a No. 1 receiver is a major negative against his case as the best corner in the game. Whether you agree with them or not, it's nice that we have to think about things like that.

Darrelle Revis made tracking receivers fashionable, both schematically in NFL circles and among the fans that took his performance doing it as the benchmark for ‘shutdown corner’ play. Several of the game’s top corners are now asked to perform a similar shadowing task to follow an offense’s best receiver, but Sherman is not among them. The Seahawks don’t need or ask Sherman to track an opponent’s top receiver, but it isn’t because they don’t believe he can do it – it’s because they believe philosophically their defense is in better shape if he doesn’t.

Moving your best cover guy around to try and neutralize the most dangerous threat makes sense on the face of it, but it puts a lot of stress on the rest of the defense and in order to best exploit it you need to be prepared to get very creative elsewhere.

The Jets under Rex Ryan were the perfect defense to take advantage of a guy like Revis at his best. They run a reasonably unusual defense to begin with and they were only too happy to adjust things in major ways that other teams might balk at. Moving one corner around can't happen in isolation. By definition you need at least one other guy that can move too and potentially a third if you are going to track to the slot.

The Jets were able to exploit Revis tracking his man because they had Antonio Cromartie on the other side who was also capable of doing it. If you don’t have that, you end up with a corner in over his head being asked to move all over the field sticking to the No. 2 guy on offense. Your top guy might be matching up well with the No. 1 receiver, but your No. 2 guy is now out of his comfort zone moving all across the field and being picked on by the second best receiver.

The question defensive coaches are now asking themselves is whether it is easier to take away a team’s best receiver by matching him up with your best corner – wherever he lines up – or by leaving your best guy where he is and bracketing the No. 1 guy, taking advantage of the confidence you have in your best cover man to hold up on an island and dedicate coverage elsewhere in the scheme.

This is what the Seahawks choose to do with Sherman. Instead of asking him to move around to cover one guy, they feel the integrity of the defense as a whole is better served sticking to what they do every down and just cheating a little with the extra room he buys them.

Take this play in the Super Bowl as an example. This is ostensibly a basic cover-3 shell that the Seahawks run as a big part of their base defense. In this coverage both corners have a deep third of the field with the FS, Earl Thomas in this case, taking the middle third. Instead of the deep area of the field divided equally as it exists on the chalkboard, the Seahawks roll Thomas towards Byron Maxwell and leave Sherman with a bit more ground to cover on his own. This allows them to be sure they have enough attention on Demaryius Thomas without asking Sherman and Maxwell to swap positions to shadow him.

They can also achieve the same thing by splitting the coverage and isolating Sherman entirely in man coverage. Again Thomas rolls to the right to cover the passing strength of the formation with two receivers lined up to that side, but instead of Sherman’s deep third expanding to compensate he plays straight man coverage, essentially playing on an island while the rest of the defense plays zone around him.

When I asked Bleacher Report's Matt Bowen – a former NFL safety and one of the smartest football minds out there – what he would do faced with that choice, he said he would actually put his best cover man on the No. 2 receiver. “The reason for that is it would allow me to take away the No.2 while rolling, cutting, bracketing, etc. to the No.1 WR with the second CB and FS over the top. You could play more Cover 6 (quarter-quarter-half) and roll the “cloud” technique (Cover 2) to the No.1 WR to get a jam with safety in the deep half while your “shutdown” guy plays quarters technique on the side of the field in a press look.”

The other point worth making is that taking the top receiver away only helps the defense if you play to a certain level every down you’re tracking him. Patrick Peterson surrendered seven touchdowns through the air last season tracking receivers. Is that really taking away an opponent’s best weapon? Revis gave up just eight over four seasons of shadowing for the Jets (from his second season onward). There’s no doubting that Peterson is a very good corner, but is he really lockdown all over the field?

Take a look at what Golden Tate was able to do to him when he lined up at RCB during an encounter last season. He turns him inside out at the line and then beats him again after the catch for a big gain. If the idea is to follow the offense’s best guy to neutralize him then plays like this are a major problem.

Joe Haden was beaten for six touchdowns in 2013 performing a similar role for the Browns. Here he gets caught peeking in the backfield against the Jaguars while playing RCB and was beaten on a double move for a score that cost the Browns the game. I’m not saying either Haden or Peterson are bad players – far from it – but would the Browns and Cardinals have been better off just leaving them to play left corner and tackling troublesome receivers by schematic adjustments?

The numbers at least suggest they probably would have been. Four of Haden’s six touchdowns surrendered came away from the left side while all of Peterson’s were given up while playing a position other than left corner. The passer rating into Haden’s coverage was more than 20 points better when he was at left corner than playing either the slot or right corner while Peterson’s passer rating allowed while playing left corner alone was a pretty ridiculous 9.9.

Haden and Peterson were both asked to shadow receivers because they were good enough to take away that weapon and allow the rest of the defense to concentrate on the rest of the offense, but were they actually good enough away from left corner to justify that tactic?

When the debate between Sherman and Peterson came up, the criticism Sherman always received was that he doesn’t track receivers. While it’s true that he certainly doesn’t do it often, Sherman has played positions beyond left corner, and usually when the offense lines up in unbalanced formations.

Take this play against Carolina. That’s Sherman lined up against Steve Smith in the slot to the right of the formation playing off-man coverage. How did his numbers stack up moving around? Though we’re dealing with a much smaller sample size than the other two, Sherman gave up a passer rating of 36.9 while playing his usual spot of left corner but that dropped to 14.2 when he was targeted in other positions.

Here is another example where he has lined up in the slot against Larry Fitzgerald. Now this is a pretty ugly throw from Carson Palmer, but watch how Sherman rides Fitzgerald downfield, watching the quarterback but also feeling for the break in the route by maintaining contact the whole way – He is then able to become the receiver when the ball is in the air and beat Fitzgerald to the ball for an interception. This is top-level stuff from a guy who doesn’t shadow receivers often, but was excellent when asked to do it.

In truth, there is no way to measure how difficult it is for a corner to shadow a receiver and what effect that has in statistical terms on his performance. I reached out to a few NFL defensive backs to get their opinion and the response was mixed. Denver's Chris Harris, a very good corner in his own right and one who has had experience playing both slot and wide, told me “Last year I played outside and inside which is way harder than playing outside the whole game. I got the experience of just playing left corner at the end of the year and it made my job way easier. It's hard to get comfortable moving around and there are a lot more routes you can see. If you just play outside there's only handful of routes your gonna see”

He did make another interesting point, though, that I hadn't considered previously: “But going against one dude and preparing for just one receiver is easier to me than having to cover multiple receivers a game.” Though the guy you're being tasked with tracking is likely the best your opposition has to offer, you do at least get the benefit of learning his nuances and moves in far greater depth than you do if you're facing three or four receivers in a game.

On the other hand, another NFL corner told me “I don't think it's too tough… it's covering.”

The bottom line is that it's an unmeasurable factor in all of this corner and coverage evaluation. We will never know how much little things like feeling comfortable and the muscle memory of certain positions aids in a corner's performance. Sherman and Revis are both able to post fantastic coverage numbers and also force quarterbacks to continue to throw in their direction – Revis through shadowing their favorite target and Sherman by being left on an island as the Seahawks lean coverage away from him – but maybe Sherman's comfort level and familiarity with the one position is what has allowed him to post the gaudy interception totals that Revis never has.

The unfamiliarity that comes with changing positions down to down introduces a split second of hesitation in Revis' play that moves him from interceptions to just passes broken up. Or maybe Sherman just has a knack for picking off passes that Revis doesn't.

Whether that is true or not Revis remains the standard by which we measure shutdown corners in today's NFL. The +33.2 coverage grade in 2009 is the highest mark we have ever given a corner and it speaks volumes that he was able to grade well last year despite being far from 100% (by his own admission) and placed in an ill-suited scheme.

With the Patriots we'll likely get to see Revis do more of the shadowing of receivers that brought this whole topic into the public consciousness.

Richard Sherman and Darrelle Revis are the two best corners in the game today. Sherman won't be asked to shadow receivers anytime soon and so this debate will always feature an intangible element, but how much of a factor is tracking receivers in the evaluation? I'm still not sure, but it certainly doesn't take Sherman out of the conversation, merely gives us something to think about.

Follow Sam on Twitter: @PFF_Sam

