When the Chargers traded Antonio Cromartie to the New York Jets it left an opening on the roster for another cornerback. However, it did not leave an opening at Cromartie's old position because the Charger's already have his heir apparent in Antoine Cason. Cason was a 1st round draft pick by the Chargers in 2008. He spent some time playing the nickelback role for the defense, but was removed from that spot during the 2009 season. Some might ask how the Chargers can expect a guy who lost his job at a lesser position to now become a starter at a more critical position? I have the answer.
First off, you can say that Cason will improve with another year under his belt or you could say that Cason wasn't that bad, but the team really like Steve Gregory. These things may be true, but there is also another truth. The nickelback position is not the same as the starting cornerback position. Sure, there have been many successful nickelbacks who became cornerbacks, but I'd argue that there are a number of successful cornerbacks who never played nickel and maybe it's because they couldn't.
More about the nickelback and cornerback positions after the jump.
The first big difference between the two positions is that the cornerback has a extra defender that is always helping him. That defender is never out of position, he never gets tired and when a defender enter his space he never misses a tackle. That defender is the sideline. Any good cornerback will use the sideline to get an advantage. He can push a receiver towards it within five yards of the line of scrimmage. He can redirect a receiver's route towards it by using his body to keep the receiver from running away from it. He can also push a receiver towards it as he is trying to make a catch and with no more force out rule the play will be ruled incomplete if the receiver doesn't get both feet in bounds with possession of the football. The nickelback rarely gets to use the sideline.The nickelback lines up in the slot (between the corner back and the defensive line). The receiver he is covering could be the third best receiver on the team or he could be the best. He could be a running back or a tight end. In today's modern NFL there is a lot of role specialization and the slot receiver may be a guy like Wes Welker who has a skill set specifically suited for lining up in the slot. Usually, the best way for the nickelback to start his coverage is to line up close to the line of scrimmage near the slot receiver.
In coverage the nickelback usually won't have to do a lot of full speed backpedals or have to turn and run to cover a Go route (where the receiver just runs as deep as he can). This is because a safety is usually behind the nickelback and he'll be in charge of taking over on any deep routes. This safety is much closer to the slot receiver than he is to the other receiver on that side so it usually isn't in the offense's best interest to use the slot receiver as a deep threat (although play action passes and other techniques that manipulate the safety can change this). So, basically what the nickelback will focus on is a lot of comeback routes, inside slants and out routes toward the sideline. Since this is the case, the nickelback will need to be suited to handle these routes first and his secondary talents can focus on the less likely scenarios.
All three of the routes I mentioned in the previous paragraph (comeback, slant and out) are what can be called timing patterns. The quarterback wants to throw to the receiver at a particular point in his route. He'll want to do this because the route is supposed to give the receiver an opening to catch the ball and run with it at that point. One way to do this is to jam the receiver within the first 5 yards. A good jam will almost completely eliminate the ability to throw a comeback route. The receiver will be in the wrong place, the defender will be right next to him and the quarterback will have to wait until the receiver is more open thus giving the pass rush time to arrive. A good jam on an inside slant route can force the receiver into the traffic that is around the line of scrimmage. This will create obstacles that the quarterback will have to throw between. However, a jam on an out route towards the sideline isn't going to help as much. It will change how the receiver runs his route, but he can still get to the same point in the route pretty easily. The nickelback will need to chase, locate the ball and get in the way of its path to the receiver.
The nickelback will have other responsibilities too. When the nickelback is in the game the defense is very spread out and it makes them a little vulnerable to the run. The nickelback is the closest defender to the running back outside of the lineman and linebackers. He'll have to be able to make some plays in run support. In addition to that, an aggressive defensive coordinator will also use the nickelback to blitz. This may be to help with the run support situation, but it may also be used to get to the quarterback in a situation where they need more than just a couple yards (and thus the slot receiver can be covered by the safety possibly with help from a linebacker dropping into coverage). The nickelback may also be needed for underneath coverage when the outside cornerback has to run deep and the nickelback becomes in charge of everything thrown short on his side of the field, which could even be the outside receiver running a comeback route.
So what primary skill set does that leave us with? He needs to be strong and able to jam. He needs to have good ball skills to knock down or intercept passes. He needs to have good speed in short bursts (as opposed to top end speed). And he needs to be able to chase and tackle a running back or quarterback. These are not all the same skills as a cornerback. The cornerback has to have great top end speed to run with the fastest players in the league on deep routes. The cornerback also needs almost a sixth sense of when he's going to have safety help and when he won't. He needs to be able to get some kind of jam, but more importantly needs to turn and run with the receiver once the jam is complete. He needs to be strong at back pedaling so that he can react to any of the receiver's short routes while still in position to turn and run deep. And, finally, like the nickelback, needs good ball skills to stop a pass. Tackling could be considered a secondary skill since most tackles will be made on a receiver who is busy trying to catch the ball. Jamming is almost secondary. Having a good short burst is secondary. Obviously, the best cornerbacks will be good at all those secondary skills, but one could argue that a player who is good at the primary skills, but below average at the secondary stuff would be an average cornerback in the NFL.
So, with that information, in a couple of days we can peek at the rankings for the cornerbacks in the draft and also look for a couple of guys that may fit the nickelback role better than the cornerback role.