Playing the slot or “nickel” cornerback position is perhaps the most difficult on defense. It requires specific traits that not all athletes possess, which is why the position is far more valuable than the perimeter cornerback. It is also why there's so much debate over former LSU cornerback Tyrann Mathieu, a troublesome but talented defender that was once known for his instincts and playmaking skills from the slot position.
Generally speaking, a slot cornerback has to be quick-footed, willing to tackle, disciplined in his technique and have a complete understanding of the offensive and defensive structures.
A quick-footed corner, which can also be described as “agile”, has to ability to mirror slot receivers throughout the route and make abrupt cuts when a move is made by the receiver. The willingness to tackle is something that unfortunately not all cornerbacks have, but those that do are prized – that is if they can actually tackle. Discipline and understanding of both sides of the ball is very important because the slot cornerback has to know where he has help – whether it's inside, out or over the top from a safety – and the opposition's common pass concepts. The most recent example of an ideal slot cornerback is Casey Hayward of the Green Bay Packers.
Although LSU's Mathieu doesn't have the same talent as Hayward does, he does have the traits to be a nickel cornerback in the NFL.
In 2011, Mathieu's final season playing football in college, he was used in various areas of the field. Many believe he was only a slot cornerback, which isn't true based off of six games I charted during that season. The numbers indicated the following:
Slot – 66 percent
Safety – 6 percent
Perimeter – 28 percent
As one can see, more than 60 percent of Mathieu's snaps were indeed in the slot, which includes boundary (short side of field), field (wide side of field) and when the ball was in the middle of the field. However, 28 percent of his snaps were also outside, which also includes the two categories of boundary and field. Overall, he spent more time in the wide side of the field than the short side as a perimeter corner while the opposite when in the slot.
As far as production, he appeared to be more disciplined as a defender outside than inside because he had less help. His technique was also superior, but it's unlikely that he spends much time on the perimeter in the NFL due to his lack of size and strength.
His strength is one area, along with discipline and patience, that will need to improve in the pros. When he attempted to bump-and-run bigger receivers in the slot, such as former Tennessee WR Da'Rick Rogers, Mathieu was overpowered despite proper technique, as one can see below.
Mathieu, who was initially lined up directly across from Rogers, slid to his left when the receiver released outside. Mathieu then put his arms up and out to jam Rogers. This was the right technique because he didn't open his hips up early and was prepared with his hands.
He could have done a better job bending his knees in this situation but nonetheless, his technique was good. When he extended his arms to jam Rogers, he was quickly met with a straight-arm from Rogers that knocked him off-balance.
As a result, Mathieu was beaten to the inside by Rogers, who caught the football from the quarterback.
Mathieu's lack of strength was illustrated on tape on multiple occasions and further supported by his four reps of 225 pounds at the NFL Scouting Combine. It's an area that he undoubtedly needs to improve on but it's not the only one.
He has to also improve on his patience and discipline as a defender. Patience is very important in a cornerback because one must mirror the route as it develops, not before it has developed. One problem that Mathieu's had is that he's too quick to open his hips and let the receiver run his route. That makes it very difficult on him to defend because the receiver has been given a free release into his stem, thus putting Mathieu in a trail position. In comparison, see how Texas' Kenny Vaccaro was disciplined against West Virginia during this past season.
Discipline is also important and is a part of the previously mentioned understanding of both sides of the ball. Mathieu needs to know where he has help and where he doesn't. If he doesn't have help outside, then he can't be overaggressive in attacking the inside. In a 2011 game against West Virginia, Mathieu was charged with covering Tavon Austin, an explosive playmaker from the slot, and got beat to the outside on a pivot route. The reason? He bit too hard on the fake inside.
Overall, Mathieu shows the physical talent and mentality to play in the slot. He has quick feet to mirror routes and a willingness to tackle but needs to continue improving his patience and understanding of where his help is.
At LSU, he played in a lot of zone coverage, which he did well in, but when isolated in man coverage, he had issues. They can be corrected through coaching, assuming Mathieu is open to coaching and willing to work hard. If he's going to make in the NFL, he'll have to be both, especially when playing the slot position.