If the play of the New England Patriots' secondary hasn't been consistent, there's a good reason: the team has had to shuffle in several different players in several positions due to injuries, leaving their defensive backfield constantly changing.
The defense has had to deal with a variety of injuries: cornerback Ras-I Dowling is now on injured reserve after tearing a muscle in his thigh for the second straight season, safety Patrick Chung has now missed two games with a shoulder injury, and safety Steve Gregory has been out since Week 4 with a hip injury. As the bumps and bruises have built up, the team has had to shift around players, starting two different configurations in the past three games and rotating players in and out of unfamiliar positions. All the mixing and matching has led to an unfamiliar bunch, and the team has allowed 42 pass plays of 20 yards or more - the most in the league. Bill Belichick spoke on the rotating door in the defense:
"I think (Devin McCourty) can handle the movement, but I think the more consistent we can be as a unit, then that builds their communication and better teamwork between the players that are involved," Belichick said. "There are always going to be some moving parts -- there are moving parts every week, because of the team that we play. And unfortunately we’ve had -- like every team does -- guys go in and out for various reasons. So it’s not perfect."
McCourty has shifted from cornerback to safety after the injury to Chung. There's also a lot of youth rookies Alfonzo Dennard and Tavon Wilson have been bumped into the starting rotation with fellow rookie Nate Ebner also receiving lots of playing time.