Detroit Lions safety Glover Quin is in the fourth year of his five-year, $23.5 million contract. But by living on just 30% of that salary and investing the other 70%, Quin has managed to double his money.

In a fantastic story from Michael Rothstein of ESPN, Quin said his frugal tendencies and savvy investments — from the moment he entered the NFL in 2009 — had allowed him to effectively earn two contracts simultaneously.

"To sit here and say I've played for eight years and made this much money, I was in a couple investments for five years and kind of made the same amount of money," Quin told ESPN. "It's kind of like having a double NFL career, you know."

Whereas so many professional athletes blow through their huge contracts and quickly go broke, Quin has set himself up nicely for the future. He majored in business at the University of New Mexico, and he told ESPN that even living on 30% of his salary still felt like a ton of money to him.

From ESPN:

"I like to call it tunnel vision. It's not good to have tunnel vision on the field, because you need to know what's going on around you, but when you're in life, especially in this field, you need to have tunnel vision, because you see so many guys around you buying cars, buying jewelry, doing this, spending money, talking about the money that they spend.

"And you're sitting there like, 'Man, I'm living off this much money every month, and this cat spending this much money every day.'"

For the first three years of his career, Quin lived on $6,000 a month, and he invested the rest of his salary in well-known, publicly traded companies. His teammates called him cheap, but he stuck with his plan.

When he signed his contract with Detroit in 2013, he did not go out and spend wildly; he did not even buy a new car (he continues to drive his 2009 Yukon Denali). Instead, he diversified his portfolio and began taking more investment risks.

From ESPN:

"After signing a free-agent deal in Detroit in 2013, Quin decided to venture into a more risky investment world — private equity, using 10 to 20 percent of his wealth to fund private, up-and-coming businesses ...

"So far, the strategy has worked. Quin and [financial adviser Humble] Lukanga estimate a five-year projection where his private portfolio could match the money he has made in the NFL. When his contract expires after the 2017 season, Quin will have earned more than $21 million, before taxes, in his eight-year career."

Quin insisted to ESPN that he was a football player first, but the time and research he puts into his investments certainly sound like a full-time job. He has a methodical four-step plan before investing, and he aspires to give money only to companies he believes are trying to change the world.

He wouldn't share his full portfolio with ESPN, but some investments listed were Health Warrior, which makes food out of chia; pawTree, a pet nutrition company; and PeerWell, whose PreHab mobile app helps patients prepare both physically and mentally for surgery to recover faster.

In some ways, Quin is using his football skills as an approach to his business. Said Manish Shah, the cofounder of PeerWell:

"I think Glover is taking his on-the-field thinking and applying it to what he does off the field. Like anticipating how a market will develop, it's very similar to how a play develops on the field. It may not happen as fast, but having the skill set to see it happening in real-time is valuable."

And Quin has no plans of slowing down.

"It's one of those things that's very exciting," he said. "Hopefully, everything continues to work out great and I can be one of those stories that they say, 'You know what, I probably made more money investing than I made playing football.'"