Dan Graziano breaks down the ripple effect Saquon Barkley's four-year, $31.2 million rookie contract with the Giants will have on the league. (0:53)

With the flick of a pen, Saquon Barkley became one of the NFL's top-paid running backs before ever taking an NFL snap. That's the result of being the No. 2 overall pick out of Penn State.

Saquon Barkley's rookie deal makes him one of the NFL's top-paid running backs at an average of almost $8 million per season. Only Le'Veon Bell (franchise tag), Devonta Freeman and LeSean McCoy average more. AP Photo/Frank Franklin II

The New York Giants signed Barkley on Sunday to a four-year, $31.2 million rookie contract, according to a source. First-round rookie contracts are guaranteed. The deal also immediately pays out $15 million, a significant chunk negotiated by his Roc Nation agent Kim Miale. It's believed that the immediate payout is the largest in at least five years, since the rookie wage scale was changed in 2013.

Barkley is the first of the top four picks in this year's NFL draft to sign his rookie contract. No. 1 overall pick Cleveland Browns quarterback Baker Mayfield remains unsigned.

Barkley signed his deal on the day when Giants rookies were scheduled to report for the start of training camp. Rookies and select veterans take the field for their first practice of the summer on Monday.

Barkley immediately becomes one of the NFL's top-paid running backs at an average of almost $8 million per season. Only Le'Veon Bell (on the franchise tag), Devonta Freeman and LeSean McCoy average more.

With compensation of over $21 million this year, Barkley will be the league's highest-paid running back for 2018.

Barkley, 21, already bought his parents a house in his hometown of Whitehall, Pennsylvania, since being drafted. This fulfilled a longtime promise. He used endorsement money negotiated for that purchase.

It goes along with Barkley's desire to follow in the footsteps of Oakland Raiders running back Marshawn Lynch and New England Patriots tight end Rob Gronkowski, who have famously decided to live on their endorsement money instead of their NFL earnings.

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The $15 million pocketed upon Barkley's signing with the Giants can instead be saved or invested.

"Once I realized when I declared for the NFL draft and kind of realized where I was going to be drafted, that was something I was like, 'You know what? Kind of want to follow the Marshawn Lynch method. I don't want to touch that,'" Barkley said on the red carpet for the CC Sabathia and Friends Celebrity Softball Game in June. "I want to invest it, put it in the right people's hands and learn as I continue to make investments. And just live off the endorsement deals."

Barkley already has deals with Nike, Pepsi and Panini America. He now has one with the Giants, too, and his concentration can turn exclusively to football.

Barkley is being counted on heavily to make an immediate impact. His presence at the first practice of camp Monday means that all the Giants rookies will be on the field for the workout.

The Giants also signed fifth-round defensive tackle RJ McIntosh on Sunday. McIntosh will begin training camp on the active/non-football illness list. The Miami product missed all of this spring because of an undisclosed illness that warranted a procedure last month.