Aight, I'm finna break this down. A couple disclaimers first. 1) I would need to watch coach's tape to get a truly accurate understanding of what was going on schematically. 2) I'm not working with him daily so I can't speak about confidence, awareness, or any other "soft" evaluation. With that said, LEGGO!
One could safely call the Patriots a cover-2 team, meaning they are in a 2-deep look more often than they are not. From this they mix in quite a bit of other stuff, but for the sake of conversation let's restrict that to cover-5 which in English is two high safeties with man coverage underneath. Let's look at what would be a typical assignment for McCourty in a cover-5. He will be playing on the outside receiver and will be aligned anywhere from on the line to seven or even ten yards off of the receiver depending on coverage. Let's assume for this coverage McCourty is rolled up. He will align his inside toe with the instep of the inside toe of the receiver, and give a "press" look. He will defend the inside release as his goal is to get into position for the trail technique which is what he is going to play in a cover-5. In the trail technique McCourty will trail the receiver by one stride and play the lower part of inside number. The inside number of the receiver is always going to move when the receiver breaks as this is essentially the fulcrum point of any cut. It will belie either the elevation or sinking of the hips which are used to make a cut. That is when the corner will know he has to play the cut and the ball will be coming quickly. This is where it gets hard. It is critical to continue to play the receiver and remain locked on through the cut, but at some point, know to accelerate when the receiver decelerates and get your head around to look for the ball. This is a catch-22 because it really sets you up for in and ups and post-corners if you look for the ball too early. Too late and they complete an easy one on you. This seemed to be where McCourty was off all year. His technique in the trail was flawless, and athletically he was perfectly able to execute his assignment. Something just looked off with his timing on getting his head around. I think him being burnt on double moves contributed to this. The other thing that is absolutely key is the play of the safety in conjuction with this. The safety has to be positioned well and get a good anticipatory jump on the ball if the corner is locked in on the receiver. A good, heads-up safety will play to this and the corner will look better as a result. Too many people view corner as an island, and from here on out I want everyone reading this to view the relationship between a corner and a safety to be a team of two. If one doesn't execute, the other will be rendered ineffective. In a cover-5, your safeties need to play downhill and play downhill quickly. That means getting good jumps on the ball and taking good angles. They had neither last year.
Another common coverage the Patriots run is the cover-3 which is a run defense. It places a safety closer to the line and shines in short to intermediate interior passes and run. They played a ton of cover-3 when they had in his prime Harrison. In the cover-3, two corners and a single safety have the upper shell responsibility. The corners will have outer 1/3rd responsibility. For simplicity, we'll talk about streak and post techniques. In the streak technique, and in cover-3 technique the corner will generally play off, providing a good cushion. The corner will usually let the receiver reach him in his backpedal, then aggressively get his hips around and run stride for stride with the receiver, aiming to squeeze him towards the boundry when defending the streak. It makes it a harder throw and takes out the inside break better. If your corner has adequate speed and hips he should only get beat by the steak if he is too slow. McCourty never had issues with this. Again, he is physically fine. The second technique is when settled into his zone he reads post. He must squeeze or close the post. He does this by calling post with the free safety and settling between the receiver and qb. He must accomplish this without overplaying and opening himself to the post-flag. The goal is to squeeze the angle of the post, while relying on the free safety to close the post. Once the post is committed it becomes the responsibility of the safety. The reason is that in a cover-3 attacking play, they will commonly run the post flag, and even more commonly run a post as part of a combination route. The goal is to draw the corner in with the post and exploit that with the other route. If the safety plays his technique well and the play is well communicated the corner should be able to make a play on the outside stuff. Teams completed a lot of posts against the Patriots in cover-3. If the safety is out of position, the corner will be left in no man's land and he will look to the viewer to be beat. In reality it is squarely on the safety. Again, corner-safety interaction is a tandem team in zone and it cannot be stressed enough when evaluating McCourty's struggles.
So, to summarize things McCourty had stuggles in seeing the ball more than anything this season. His timing of getting his head around was off and this is a function of teams having a season of film to break down on him. I would look to see a marked improvement in this next season as this is a reps issue. The other critical issue is his safety continuity. Athletically he was just fine and 99% of his technique was there all season, he just couldn't quite put it all together. Without good safety play with him, he was frequently stranded in no man's land and looking out of position because his safeties were either out of position or too slow to help him out. For the importance of safety-corner interaction look at how much better the secondary as a whole played when McCourty was moved to safety where he played quite well. Both corners improved when he moved there.
