THERE was a time when the left tackle on an American football team was just another anonymous giant. Now they’re among the top earners on most NFL teams. Acclaimed author Michael Lewis found out why in a fascinating new book, but discovered an incredible story along the way. Michael Moynihan reports.

READERS of a certain age may remember Lawrence Taylor of the New York Giants, an 80’s pass-rushing linebacker whose fearsome strength and speed forced defences to redefine the job description of the left tackle, the player who lined up opposite Taylor.

Previously just anonymous behemoths, those left tackles suddenly became highly prized — and rewarded — as American football coaches needed huge, fast men to defend against Taylor’s attacks on the ‘blind side’ of the quarter-back. Most quarter-backs are right-handed (including Indianapolis’ Peyton Manning and the Chicago Bears’ Rex Grossman, who contest the Superbowl tomorrow), so they can’t easily see what’s approaching from their left. When it was Taylor, he usually arrived with murderous intent.

Michael Lewis’ new book, "The Blind Side: Evolution of a Game", opens with an account of Taylor’s brutal tackle on Washington Redskin quarterback Joe Theismann in 1985, when Theismann suffered a career-ending leg-break.

However, while Lewis outlines how tactical change arrived in the professional game, he also describes how, incredibly, one black child who raised himself on the streets is now the hottest college prospect in the position. All thanks to his adoptive white millionaire parents.

"The Blind Side" deals with the changing position of left tackle, but it’s mostly devoted to Michael Oher, a 350-pound boy from the third poorest zip code in the US, in east Memphis.

Hanging around the fringes of the exclusive Briarcrest Christian secondary school, Oher caught the attention of self-made millionaire Sean Tuohy, whose son attended the school. Tuohy started off helping Oher out by buying him lunch in the school cafeteria. He ended up adopting the boy.

Lewis explains: "The Touhy family, before they met Michael Oher, had had several poor black kids who had come through their children’s private school. And Sean, because he had the experience of being the poor kid in the rich school when he was growing up, had made a point of seeking them out and seeing if they needed anything.

"All those kids had mothers who were functioning grandmothers, or someone who was taking care of them. And they had a home to live in and a bed to sleep in. Michael was unusual in that he was so exceptionally needy.

"But the kids also saw the level of need. Their parents said: ‘Look, this boy doesn’t have a bed to sleep in; he doesn’t have a roof over his head. We are just going to let him sleep on the sofa for a while.’ And then after he started putting dents in the sofa because he weighs 350 pounds: ‘We’re going to get him a bed’."

Oher’s eventual legal absorption into the family led to problems in a number of areas. Tuohy’s wife Leanne — something of a force of nature herself — had to deal with whispers about the advisability of having a huge black teenage boy living under the same roof as her teenage daughter.

When the boy began to join in basketball and football practice at Briarcrest Tuohy, an accomplished college athlete in his time, realised his huge potential. For anyone unaware of the arcane recruiting procedures of major US colleges, this part of the book is an eye-opener — college coaches are allowed to watch but not approach high school prospects, which led to surreal scenes when some assistant coaches attended one of Oher’s first football training sessions. When the youngster obliterated an opponent in a one-on-one drill it led to a flurry of mobile phone calls from the assistant coaches to their superiors, who then descended en masse on Briarcrest. But they couldn’t speak to the boy unless specifically invited to.

This led in turn to extravagant promises being made to Oher’s adoptive brother, Sean Tuohy’s son, with one coach promising him his own cubicle in the college team’s changing rooms.

The burgeoning interest led to another series of problems: the college sport regulatory body, the National College Athletic Association or NCAA sent investigators to quiz the Tuohys to try to establish whether they had offered incentives to the boy to sign for the University of Mississippi.

However, arriving in college is no guarantee of success in the professional game. Lewis points to the "brutal" system of elimination in American football.

"These are the numbers — there are a million high school football players in the country, roughly fifty-five thousand of them will play college football. And a thousand of those will have some kind of professional contract, of whom just a couple hundred will make enough money to have careers. So you are talking about a winnowing process that’s brutal.

Broadening the argument, the author points out that the rags-to-riches tale exposes huge issues in American sport and society. Oher’s talents as a footballer might never have been discovered.

"It’s a huge tip of the iceberg," says Oher. "There are all these less visible talents that go untapped. So that was really about the way inner-city America neglects and destroys value in people.

"That’s the thing that shocked me so much as I dug into Michael’s childhood. I thought I knew how bad it was. I had no idea. There was within the inner city the ghetto, there was a class system, and he was at the bottom of it. He was doomed at birth. It was an incredible stroke of fortune that he got himself out."

Within the professional game the value of the left tackle is already dropping. A new school of thought in American football holds that the centre, the player who snaps the ball from the middle of the offensive line, is the key to a successful team: he has to be athletic, strong and command the playbook, barking instructions to this fellow troops. The Chicago Bears’ Olin Kreutz is given huge credit for his side’s run to the tomorrow night’s Super Bowl.

Indianapolis’ centre, Jeff Saturday was presented with a trophy last Wednesday by as the "non-quarterback, non-running back MVP for 2006", which shows his importance to the side.

That’s nothing to do with Michael Oher, mind. His life story is now being made into a Hollywood movie — Renee Zellwegger playing Leanne Tuohy, his adoptive mother. It gets better: now twenty, he’s the left tackle for the University of Mississippi and regarded as a red-hot prospect for the NFL. Though there are no sure things in the hard world of professional sport, Oher is set up to dominate the blind side for some time to come.

The Blind Side: Evolution Of A Game, by Michael Lewis is published by Norton.