In response to neinmd's comment:
In response to Paul_K's comment:
Interesting viewpoint. What are the best benchmarks, then, to measure the effectiveness of BB's defensive strategy, if we buy into this notion? Other than point differential?
Point differential, when it really counts to both head coaches during the first three quarters and sometimes late in the game also, is the gold standard. It says that two teams tried their hardest to lay in extra chances to win the game, and one team was either a little better or way better. Point differential covers almost every angle that the coaches use to gain advantage, from kickoff defense to working the last seconds of the clock just before halftime. At the end of the game, one side tries desperate measures and occasionally the dice come up double sixes, but one double six roll isn't a statistically significant measure that the dice will roll double sixes next time.
I've heard that the average interception is worth about 40 yards, but there are excellent interceptions and marginal interceptions. If the Pats have a third and 25 and Brady heaves the ball 40 yards downfield toward Randy Moss in 2008 or Dobson now, that's a pretty good play. If a defensive player makes the interception he gets tackled 40 yards downfield, with the same result as if the team had punted on fourth down. If Moss/Dobson makes the catch it's a first down. Equal standards apply if a team is down two scores with four minutes to go. Throw it into traffic or else you lose. The Patriots' 20 interceptions aren't super significant because they've been picking off too many of the opponents' hail marys.
On a first and ten or especially on a second and one, an interception of a short pass hurts quite a bit more than on third and 25. Then there's the dreaded pick-six, worth at least two normal interceptions.
Most interceptions aren't related to the backfield's stellar play. Some are caused by overly tall defensive linemen (Chandler Jones is a prototype) tipping the ball. Some are caused by rushers pressuring the quarterback and causing a hurried throw into traffic. A defensive gambit that causes an offensive lapse may be the cause. Some interceptions are caused when a defensive player reads the play, it's been called one too many times, and jumps the route. A linebacker timing the snap count can cause an interception.
All in all, counting ints is slightly better than nothing, but a far better stat could be crafted.
Defensive yardage is another problem. On third and 9, giving up 7 yards is a victory. The whole field should be partitioned into meaningful yardage sectors, where a ten yard gain far from field goal range is less meaningful than a ten yard gain that gets the team just about into field goal range, and where a trip from the opponent's 25 yard line to his 15 is far less meaningful than a first down trip from the opponent's 11 to his 1. Then comes the inevitable dive over the top, which is a really big defensive yard if the defense ever stops it.
If I ran an NFL team I'd have tons of more meaningful stats, where the calling of every play was designed to maximize my team's chances of eventually winning the game. We peons on the outside don't have those numbers. What we have are the numbers which are easiest to calculate. That doesn't mean the numbers are any good.