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By Kerry J. Byrne, Special to SI.com, ColdHardFootballFacts.com

Bill Belichick's legacy cracked apart last year like the lobster claws at a Gillette Stadium tailgate.

The trouble should have come as no surprise. After all, the flaws in his game have been simmering for the better part of the 21st century. They finally boiled over in the fourth quarter of Super Bowl XLII, spoiling what should have been the greatest celebratory feast in New England since 1621.

These cracks in Belichick's legacy have nothing to do with Spygate" or the off-the-field issues perpetuated by the pigskin pundits or splashed across the gossip pages of the gridiron.

Instead, the cracks in Belichick's legacy have everything to do with what's transpired on NFL football fields over the last several years as he stalked the sidelines. Let's put it this way: When your defense surrenders a gruesome 54 fourth-quarter points in four Super Bowls, as Belichick's defenses have, it will tend to tarnish a rep here and there.

Still, Belichick has been considered the singular defensive genius of his generation. Some pundits even argued, right up until about 10 p.m. on Feb. 3, that he was the greatest coach of all time. Raise your hand if you heard that one in the run-up to the Super Bowl? Anyone? Anyone?

That's right. We see ya. We heard it, too.

Belichick is still a great coach. The greatest of his generation. If you have evidence to the contrary, by all means, send it our way so we can examine it and ridicule it.

But the savory flavor of the Belichick legacy has been soured by on-the-field issues too large to ignore. In fact, if he fails to win another Super Bowl, Belichick might not be remembered for the three Super Bowls in four years. Instead, he might only be remembered for what might have been. He might be remembered for ...

1. The big-game defensive implosions

Despite Belichick's reputation as a defensive mastermind, his defenses have habitually reserved their worst performances for the biggest moments in the biggest games.

In fact, Belichick has overseen some of the greatest defensive catastrophes in modern NFL history, a series of gridiron Hindenburgs that explode live on national television year after year as all of New England cries out for humanity. Consider these fourth-quarter debacles:

• Super Bowl XXXVI (Patriots 20, Rams 17) -- Hardly a colossal breakdown, but the cracks began to show in the Belichick legacy -- ironically -- at the furious end of this, his greatest triumph. The Patriots held the Greatest Show on Turf to three points through three quarters. At one point, it even looked like a rout: a fumble return for a TD by New England defensive back Tebucky Jones would have given the Patriots a 24-3 lead late in the third quarter. But the play was overturned by a penalty against the defense.

The Rams stormed back, scoring two fourth-quarter touchdowns -- following their two longest drives of the game (55 yards and 77 yards) -- to force a tie with 90 seconds to play. If not for the what became typical Tom Brady heroics, leading the only walk-off scoring drive in Super Bowl history in just his 17th NFL start, this game might be remembered only for New England's defensive collapse.

• Super Bowl XXXVIII (Patriots 32, Panthers 29) -- The wheel's began to wobble on Belichick's defensive wagon here in Houston. The 2003 Patriots boasted the league's No. 1 team (14-2) and No. 1 defense (14.9 PPG). The 11-5 Panthers, meanwhile, had mustered just 10 points through three quarters against this, the league's best defense.

But, when it mattered most, Belichick's defense snapped more gruesomely than Joe Theismann's tibia. The spunky little Panthers ripped off three TDs, 19 points and 251 yards of offense -- in the fourth quarter alone. The Confederates played better defense during Sherman's March to the Sea.

To put those 19 points into perspective, consider it was the greatest single-quarter total the Patriots had allowed in a well over a year. To put those 251 yards into perspective, consider New England's No. 1 scoring defense had surrendered an average of just 292 yards per game all season.

Belichick's legacy survived the meltdown, as the New England offense responded with a remarkable 11 points in the final four minutes, including another last-second field goal, to stave off a humiliating upset to an inferior opponent.

• 2004 AFC Championship Game (Patriots 41, Steelers 27) -- A pigskin portent of things to come reared its head here in the 2004 AFC title tilt. It was the coldest game in Steelers franchise history. Yet the Patriots offense made a mockery of the weather and Pittsburgh's No. 1 defense and largely controlled the game.

In fact, this could have been a four-TD rout. But Belichick's defense simply could not get off the field in the second half, again when it mattered most. The Steelers, after scoring just three first-half points, ripped off three TDs and a field goal in just five second-half possessions.

You might have expected New England 's offense to struggle on a bitter night on the road against a hostile crowd, against the elements and oh, by the way, against the league's best defense. Instead, Brady played his single greatest game, and the offense carried the day, scoring 41 points against a team that had not allowed more than 30 all season.