Guys who don’t get to play much, Mr. Jackson notes, get pretty worked up when they are allowed onto the field. During one preseason game, he is put in for a few plays late in the contest, when everyone else is going through the motions. “I run around like a crazed jackal,” he says. “I want blood. I want to taste the iron on my tongue as I rip the flesh from a safety’s bones and play Hacky Sack with his testicles. Everyone looks at me like I’m an idiot.”

Mr. Jackson dislocated his shoulder twice in college, and now it keeps popping out of the socket. When this happens in a practice, “it feels, strangely, like my head is on backwards.” Dislocated shoulders are the least of it. He seems to break, bend or twist every bone in his body. “Pads and helmets crack,” he says, “creating a frightening symphony of future early onset dementia.”

Doctors patch players up, usually with shots of painkillers. Mr. Jackson’s favorite painkiller is a natural and often organic one, and he makes a lovely argument for its benefits: “The N.F.L. should remove marijuana from their banned substances list. Don’t tell anyone about it: just stop testing for it. Pain is a big problem in the N.F.L.”

He continues: “No one ever overdoses from weed. The problem is pills and booze. A joint can alleviate the need for either and plant buttocks firmly on the couch, where a ‘MacGyver’ marathon takes on epic proportions.”

About pain and the media, he notes how players are schooled to talk to reporters. “Do say: We’re taking this thing one game at a time and we’ll see what happens. Don’t say: Man, I really would like to go home and eat a heroin sandwich.”

Mr. Jackson says he saw no evidence of steroid use in the N.F.L., but by the end of the book, injured and with his career in the balance, he briefly injects himself with human growth hormone before abandoning the idea.

Image Nate Jackson Credit... Tom Jackson

He loves football; he thinks it’s a beautiful game, even though he’s being used, and his body is taking a pounding. “The good/bad thing about football,” he observes, “is that it moves too quickly for your conscientious objections to keep pace.”