I don't believe that Belichick enters a game determined to hold back, to run a vanilla defense so he doesn't give anything away for the future.
The games are usually too close for this.
Belichick is all about one game at a time. What is the best defense to counter the problems this specific offense offers? Let's win this game, and then move on.
If 'releasing the hounds' means blitzing, then they blitz when they feel it's an advantage. In the Jacksonville game, Jacksonville rarely blitzed but instead dropped most of the defense into coverage. Brady, with the extra time, hit Welker, Faulk, and Maroney, averaging only six yards per completion or so to those receivers, but with a 93% completion rate, that didn't lead to too many third downs. However, Jacksonville didn't feel that they had an advantage by blitzing. In the past, New England has used this approach against Manning, dropping lots of players into coverage. In the Jan 2007 AFC Championship Game, Manning used that defense to do the same thing Brady did against the Jaguars -- he hit the underneath guy in the middle of the field, and the receiver picked up plenty of yardage.
In the Giants game, I felt that New England decided they were not being successful in coverage and had to increase the pressure, taking the risk of open receivers. Eli Manning was more accurate and patient than they expected. They adjusted by increased blitz pressure, and were successful with the pressure in the second half. That doesn't mean that they went in with a plan of one defense in the first half, and another in the second half.
This argument essentially posits that Belichick says:
We want to let them score a couple times in the first half.
That's absolutely crazy.
Belichick would like to score every time they have the ball, and stop the opponent every single time they have the ball.
Now, another, different, question is:
Have the Patriots showed all the defensive schemes they are capable of yet?
The answer to that question is no.
Recall the Philly Superbowl year.
They played Pittsburgh by attacking their safeties, going over the top, and running a high-scoring offense, forcing Pittsburgh to try to keep up.
The following week they ground it out against the Colts, keeping the score low, flooding the passing lanes with defenders, keeping the Colts in long drives.
In the Super Bowl, they unveiled a defense featuring five linebackers and only two linemen, keying on McNabb and Westbrook in space.
They showed three entirely different approaches.
But they designed a gameplan for each individual opponent.
That's the approach the Pats take.
They will design a defense for the Chargers that addresses the specific strengths of the Chargers. If it doesn't work, they will adjust over half-time.
But this isn't a case of them having a great defense, but not unveiling it.
