Bill Belichick got his first job in the NFL at age 23—it paid $25 a week

New England Patriots head coach Bill Belichick reportedly earns more than $10 million a year. But he started out at the other extreme.

Belichick's first job in the NFL, with the Baltimore Colts, paid practically no money.

It was 1975 and Belichick, then 23, had just graduated from Wesleyan University. A college coach of his put in a good word with Ted Marchibroda, the head coach of the Colts at the time.

"Bill Belichick interviewed with Marchibroda and told him he wanted to work 14, 16 hours a day, and that he'd do anything his boss asked of him," Ian O'Connor reports in his 2018 book, "Belichick," adding: "Marchibroda thought the kid sounded sincere enough and took him up on it."

The gig, which involved everything from analyzing game film to driving the coaches around and working the Xerox machine, was originally unpaid. Still, in Belichick's eyes, it was a sweet deal.

"I got three meals, a bed, and a lot of football," he told O'Connor, "and that was all I really wanted at the time."

Plus, what he learned as part of the team's small staff amounted to "a graduate course in football," Belichick told O'Connor.

The young man impressed his superiors and, after just a few weeks, the Colts general manager offered to pay him $25 a week, or $21.22 after taxes, O'Connor reports. Although he didn't have an official title and was working as an "apprentice," players considered him "an integral part of the team," O'Connor writes.

"Belichick was as detail-oriented as any of the veteran coaches on staff."

Though he was young and had no experience, Belichick wasn't intimidated by the pro players. As he told CNBC's Suzy Welch, during a team meeting that season, two teammates, including a talented starter, spent the beginning of the meeting chatting and joking around. Inside, Belichick said, he was seething: "I'm not afraid of these guys. It's either [them] or me. We can't run a team like this."

Finally, he erupted: "Look, either you shut up or you get out of here. That's it."

It did the trick — and it was in that moment that he learned effective leadership requires being the boss. "I don't care if they're a star player," he told Welch. "I don't care who they are. You have to set the tone."

By the end of his 1975 season with the Colts, Belichick was earning $50 a week, and he wanted a raise heading into the next season. He asked for a $4,000 salary and a car. The general manager wouldn't budge.

Another team was willing to pay him to be an assistant, though: The Detroit Lions "stole him away with an offer of $10,000," O'Connor writes, and "a new Thunderbird."

Don't miss: 5 rich NFL stars who live like they're broke

Like this story? Subscribe to CNBC Make It on YouTube!