Lewis’s subject is the salvation of Michael Oher, a black child virtually raised on the mean streets of Memphis. But Lewis also continues what he began with “Moneyball,” his 2003 best seller explaining new thinking about how to construct baseball teams. He is advancing a new genre of journalism that shows how market forces and economic reasoning shape the evolution of sports. Oher, who today plays left offensive tackle for the University of Mississippi, is a valuable commodity because of the lasting impact on football made by someone who played on the other side of the ball.

After the 1981 regular season, Lawrence Taylor, linebacker for the New York Giants, became the only rookie ever named the National Football League’s defensive player of the year. He was 6-foot-3, 240 pounds and quick as a cat, running 40 yards in 4.5 seconds. He was, Lewis says, “a new kind of athlete doing a new kind of thing.” This is how Taylor described his thing:

“I’ll drive my helmet” into the quarterback, “or, if I can, I’ll bring my arm up over my head and try to ax the sonuvabitch in two. So long as the guy is holding the ball, I intend to hurt him. ... If I hit the guy right, I’ll hit a nerve and he’ll feel electrocuted, he’ll forget for a few seconds that he’s on a football field.”

Terrifying, disorienting and injuring quarterbacks is most of a linebacker’s job description. Taylor concentrated coaches’ minds on the problem of protecting quarterbacks. Most of them are right-handed, which means that when they are passing, threats from their left come thundering at them from their blind side. Hence the sudden interest in large and agile left offensive tackles. This interest intensified when Bill Walsh, coach of the San Francisco 49ers, devised the West Coast offense. It floods the secondary with receivers. More receivers mean fewer pass blockers, so the left tackle has more problems to cope with.

Which is why by 2004 the average salary of an N.F.L. left tackle was $5.5 million a year, second only to the average for quarterbacks. The five most highly paid left tackles were earning almost $3 million more than the five most highly paid right tackles. That is very good news for Oher, one of 13 siblings from the nation’s third-poorest ZIP code.

He had finished the 9th grade, but the 10th was unlikely, and he was on track to be selling drugs, en route to jail or an early grave. His father was long gone, his mother was in and out of drug rehab. In his file from the public school system — he had been in 11 different schools in nine years — the numbers looked, Lewis says, “like misprints.” His measured I.Q. was 80; his “ability to learn” placed him in the sixth percentile. He had repeated first and second grades. The school system said that through the fourth grade he had performed at “grade level,” which is odd because he never attended third grade. He was almost nonverbal. Essentially unparented throughout his childhood, he scavenged for clothes, slept here and there in (sometimes slightly) less disorganized households than that of his mother, who when Michael was 5 was caring for seven boys and three girls, all under 15. Caring, that is, in her fashion. And not at all for 10 or so days after the first of each month, when her welfare check arrived and she disappeared to feed her addiction to crack cocaine. On one occasion, lasting for weeks, his mother and seven boys slept in an old Chevy, washing themselves in a service station bathroom. For five years he lived in various households in a housing project with about a thousand residents and “no two-parent families: zero.” It is unsurprising that Oher, according to Lewis, became a teenager who “didn’t know what an ocean was, or a bird’s nest, or the tooth fairy.”