Up until this past week, Patriots safety Devin McCourty had looked brilliant in his transition to his new position from cornerback. His solid play at safety has helped the Patriots to mitigate the damage done against them on deep passes.
On Sunday, his worst game at safety this season saw those early-season problems make a not-so-triumphant return.
When McCourty plays with good technique and sticks with his assignment, he is well above-average at safety. In fact, despite having played jut 564 snaps, ProFootballFocus.com ranked McCourty as their 13th-best safety in the NFL.
His night wasn't entirely bad; he had a very timely interception in the end zone that helped New England mount its near-comeback, but he was on the receiving end of at least a pair of plays that landed New England in a 28-point deficit in the first place.
The first time is the most notable, against former Patriots wide receiver Randy Moss.
The 49ers ran four vertical routes against a six-man rush by New England, leaving the four defenders in man coverage along with McCourty in Cover 1 on the back end.
It's not entirely McCourty's fault; cornerback Alfonzo Dennard didn't help much in failing to get a jam on the receiver at the line, but McCourty chose to stay closer to the middle of the field while two wide receivers ran vertical routes to his right.
This snapshot shows 49ers quarterback Colin Kaepernick staring at the left side of the field; he didn't even try to look McCourty off. Once the safety moved to the middle of the field and turned his back to the receivers on the right, Kaepernick knew he could throw it with confidence.
As mentioned in this week's progress report, the Patriots hadn't allowed a passing touchdown of 20 yards or more since Week 11 against the Colts. As mentioned in this week's progress report, the Patriots hadn't allowed a passing touchdown of 20 yards or more since Week 11 against the Colts. After giving up a league-leading 10 such touchdowns through Week 8, the Patriots had built a dam on the back end and hadn't sprung a leak since.
The 49ers opened the floodgates, though, with four 20-plus-yard passing touchdowns on Sunday night.
The Patriots defense was in Cover 3, a zone defense with three defensive backs deep accounting for a third of the width of the field. This time, Kaepernick baited McCourty to the offense's left, taking him off his assignment to cover the middle third of the field.
McCourty moves to the right side of the defense to help out in coverage on Moss, which leaves Dennard in an impossible situation of covering both receivers.
He's in no man's land, and Kaepernick exposes him after coming back across the field.
It wasn't all bad for McCourty; he had an end-zone interception against the 49ers to pair with an end-zone interception he had the previous week against the Texans.
The Patriots sent a five-man rush at Texans quarterback Matt Schaub, with the defensive backfield playing man coverage and with McCourty in deep zone.
There are two vertical routes headed at McCourty, so he must be in position to defend both of them.
Instead of his hips being turned away from the line of scrimmage, he kept them square. His discipline to stay in the middle of the field allowed him to break on the ball once Schaub released it.
He didn't have to take a chance, instead simply fulfilling his assignment, yet he still came away with the play.
ESPN analyst Jon Gruden commented on what he saw on the broadcast:
Well McCourty makes a great play—a range play ... Matt Schaub, I think, was surprised by the range of McCourty ... but that's why Bill Belichick moved Devin McCourty back to free safety—he has tremendous range. Belichick loves those hybrid safeties that can cover slot receivers, play physical against the run and do it all.
One of the highest compliments Belichick gives any player is that they do their job. It's what he constantly asks his players to do, and "do your job" has even become a slogan synonymous with Belichick as a result.
What did he have to say about McCourty earlier this year?
...Devin has been a solid, dependable player for us for three years now in different roles. I think that he’s performed and has and continues to perform at a good, high, solid level. Is he more comfortable now than he was a couple weeks ago because he’s played more? He probably is, but I thought that he did a good job when he stepped into that role. Like every player, the more you do it, there has to be a higher level of repetition and confidence and reaction time and all of those type of things. I’m sure that it helps to some degree.
When McCourty is on his game, the Patriots have a great answer to their problems at safety.
While Sunday's performance didn't invalidate the switch to safety, it did serve as proof that McCourty isn't flawless at his new position just yet; he will have to show against the Jaguars and the Dolphins that last week's mishaps were a fluke.
Erik Frenz is the AFC East lead blogger for Bleacher Report. Be sure to follow Erik on Twitter and "like" the AFC East blog on Facebook to keep up with all the updates. Unless specified otherwise, all quotes are obtained firsthand or via team press releases.