No defense

Losing Tom Brady was one thing. But as we delve into the middle of this NFL season, as the Patriots suddenly look more and more like a makeshift outfit, New England no longer looks merely like a team without a quarterback. What the Patriots seem to be, too, is a team without a defense.

And we all know where the buck stops on that one.

And so now, one week after the San Diego Chargers toasted the Patriots -- and Deltha O'Neal, in particular -- in a 30-10 San Diego win on national TV, the Denver Broncos come to Foxborough in Week 7 with the top-ranked passing attack in the AFC. On Monday night this time, America once again will be watching. And the question now is whether Bill Belichick can save this team, whether the accomplished coach of the Pats can sufficiently fill the holes on his defense that, in many ways, are far more worrisome than the hole behind center.

When Brady went down, we expected the Patriots' offense to struggle.

With Belichick here, we did not expect the defense to disintegrate.

"I don't think the competitiveness of the game was reflected in the score," Belichick said on Monday in his weekly briefing on The Day After. "We did a lot of good things but we offset it with missing some opportunities and not being able to make a few plays at the right time."

Of course, we all know what the defensive formula has been in New England over the last several years. We know Belichick's philosophies and respect his pedigree. Make the offense work. Give up yards, not touchdowns. Stay in position and take no foolish risks, because any renegade behavior could undermine the success of the unit.

Yet now, in the wake of the San Diego loss, the Patriots seem to be crumbling in an array of areas, the most surprising of which comes on defense.

Against the Chargers, the Pats allowed three pass plays of 40 or more yards and were slapped with a 32-yard pass interference penalty. They gave up three passing touchdowns and more than 300 yards in the air. That came only two weeks after the Pats were all but undressed by Miami Dolphins running back Ronnie Brown and the rampaging wildcat offense, and it all makes you wonder what the heck is happening to a team and coach that so often prided themselves on being figuratively and literally one step ahead, even when the other guys had the ball.

Especially when the other guys had the ball.

"Anytime the ball gets thrown over your head in the secondary, that's not good," Belichick admitted. "It is every defensive back's job to keep the ball in front of [him]. The intent is to never get it thrown over your head, whether [there] is a pass rush or not. That is the last line of defense. You have to prevent the big play and if they hit them, then they can hit them in front of you. Ultimately, the long passes have to fall on the secondary. You are always looking for more pass rush and tighter coverage, but you have to defend the deep ball first. We didn't do a good job of that."

Fall on the secondary?

No, no, no.

In this case, it seems to fall on the coach.

Cracks in the system
At another time, under different circumstances, O'Neal would not have been playing left cornerback at all. The responsibility might have belonged to Asante Samuel. But the Patriots have a system and it has served them well, and so Samuel was allowed to leave the club as a free agent following Super Bowl XLII. This is how things generally have worked in New England over the last seven years, where the only indispensable pieces have been the quarterback and the coach.

David Givens came and went. Deion Branch came and went. The Patriots cut loose Ty Law, Adam Vinatieri, Daniel Graham, and Lawyer Milloy, and the team kept right on winning.

It wasn't the players.

It was the system.

Over the years, despite the effects of age on the linebacking corps (Tedy Bruschi, Mike Vrabel) in particular, the Patriots did relatively little to address the problem in the draft. The understanding was that Belichick did not like young linebackers. The Pats signed Adalius Thomas before the 2007 season and drafted Jerod Mayo (finally) in 2008, and Mayo has shown promise. But he is a young player in his first NFL season on a unit that now has more problems than solutions, and you can only wonder if the Patriots settled on the right answers at the wrong times.

With regard to the Patriots' defense this season, one of two things is happening: The Pats lack either the personnel or the coaching. In either case, the accountability circles back to Belichick, who has as much control (or more) of his team's entire operation as any coach in the league. If Thomas has been a disappointment, the Patriots made the mistake of signing him. If O'Neal (or anyone else) is incapable of playing left corner, the Pats should have kept Samuel. If the defense looks old and slow, the Pats should have done a better job of preparing for the future while they were beating up on opponents with alarming regularity from 2001-07.

As the coach, after all, Belichick deploys the talent. As the chief evaluator, he selects the personnel. Belichick both buys the groceries and prepares the dinner, to borrow an old coach's analogy, and the problems with the Patriots' defense this season go well beyond the absence of a historic talent at quarterback.

They suggest bigger, deeper problems.

Could it be that Tom Brady so effectively masked deficiencies on the Patriots' defense that even the great Bill Belichick could not see them?

No defense for defensive performance
Admittedly, Belichick is an easy target. The soap opera of Spygate proved that for all of us. Belichick is a brilliant man with an uncanny ability to focus, and his personal quirks only further arm his critics. Many of them will tell you that Belichick is insultingly arrogant, that he is rigid and inflexible, that he is a social misfit with the people skills of a Pet Rock. In the end, none of it really matters, particularly to Belichick, who is nothing if not single-minded.

His ultimate goal, always, has been to win football games.

Entering Week 7 of the NFL season, the Patriots own a 3-2 record, including discouraging losses to Miami and San Diego. Those losses were more discouraging for the defense than for the offense, where the absence of Brady has a damning effect. No matter the quarterback, the Patriots were going to score less the moment Brady went down with a knee injury. They were just going to have to win differently, with a running game and special teams, with coaching and defense.

This season, so far, the Pats have had no significant injuries on defense. They have struggled just the same. And for all that Bill Belichick has accomplished here, for all that the Patriots have done, the defense reflects on him more than on anyone else because of what Belichick has made of himself and because of what he has come to stand for.

After all, he is who he is.

Tony Massarotti can be reached at tmassarotti@globe.com and can be read at www.boston.com/massarotti