In law, "the fruit of the poisonous tree" refers to the inadmissibility of evidence obtained through illegal means.

In football, it's become a good description of the coaching descendents of a certain New England genius.

In other words, he's Bill Belichick, and they're not.

That appears to be the lesson of the disappointing Charlie Weis era at Notre Dame, and the recent careers of several Belichick lieutenants.

Under their enigmatic head coach, the Patriots won three Super Bowls in four years from 2001-4. The team's offensive and defensive coordinators became hot commodities; both landed head coaching jobs before the 2005 season.

Romeo Crennel went 24-40 in four seasons running the Cleveland Browns, posting one encouraging 10-6 season but surrounding it with disheartening 4-12 ones. His supposed defensive wizardry left the Browns with worse overall rankings in points and yards allowed than they had in the four previous years under Butch Davis.

Offensive coordinator Charlie Weis received an impressive commitment from Notre Dame, six years at a reported $2 million per year. Just seven games into his first season, the university tore up that contract and replaced it with a ten-year deal worth $30-40 million. The Irish were 9-2 and 10-2 in his first two regular seasons, losing in a BCS bowl each year. Then, with teams consisting of his own recruits, Weis posted a dismal 3-9 record in 2007, went 7-6 in '08 (including a victory in the non-BCS Hawaii Bowl), and is 6-6 this season. Over the last four years, Notre Dame has gone 2-11 against ranked opponents. They've lost two of three to Navy, a school the Irish had beaten the last forty-three times they met. They lost to Syracuse in '08, the first loss ever by Notre Dame to a team with eight losses.

When Crennel left New England, Belichick promoted his defensive backs coach Eric Mangini to coordinator. One season later, Mangini was hired by the New York Jets to be their head coach - a job Belichick had held for exactly one day before resigning in January 2000. Mangini started strong with a 10-6 season, losing to New England in the playoffs, then faded to 4-12 in his second year. His third was a microcosm of the first two - an 8-3 start, a 1-4 finish for a 9-7 record. His often harsh and imperious ways wore out his welcome quickly, and the Jets fired him with a year to go on his contract. The Cleveland Browns tapped him to replace Crennel (again), and three games into his tenure there were reports that he had lost the attention and respect of his players. The Browns are 1-10 after yesterday's loss to Cincinnati, and boast the league's second-worst offense and sixth-worst defense.

Crennel. Weis. Mangini. What did or didn't they learn from Belichick that they should fail so thoroughly?

Belichick's own mentor, Bill Parcells, is a fiery figure who can be dismissive and belittling, but also knows how to motivate his players with a sly needle. He could read his locker room like a quarterback, and assembled teams that responded to his methods, playing a fierce attacking defense and a controlled, disciplined offense.

Belichick's own style is more remote. His players know that he is beyond sentimental attachment to any of them, and won't hesitate to send them packing if it suits his preferred salary structure. He has been a genius of the salary cap era, retooling continually to blend youthful athleticism with experience where it can do the most good. (Of course, all plans work better when you have Tom Brady at quarterback.)

His first term as a head coach was a disaster, just one winning record in five seasons with Cleveland, where he alienated fans and media alike with his cold condescension. Five years later, he found a better balance in New England, though he still suffers fools badly. His three quick Super Bowl wins put him beyond questioning; no other coach could have so easily weathered the uproar over his failed fourth-and-two gamble against Indianapolis, or the Super Bowl loss that derailed an unbeaten season.

When Belichick speaks, he still makes it clear that he believes he is the smartest person in the room. It's not a trait that transfers well. His former assistants should try to forget everything they learned about personal relations in their years with New England, and forge their own styles if they ever get another chance. Josh McDaniels, another Belichick protégé whose Denver team is having its ups and downs, showed his roots in unloading quarterback Jay Cutler, a move that has worked out well; so far, his mistakes are more errors of enthusiasm than arrogance.

Belichick's manner is unique, perhaps in pro football history. It works for him, because it's true to who he is.

He's Bill Belichick. And no one else is.