College football 2018: Biggest X-factor on every Top 25 team

GLENDALE, AZ - DECEMBER 30: Miles Sanders (24) of the Penn State Nittany Lions runs for a gain in the game between the Washington Huskies and the Penn State Nittany Lions on December 30, 2017 at the Fiesta Bowl in Glendale, AZ. (Photo by Jordon Kelly/Icon Sportswire via Getty Images) /

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Stanford quarterback K.J. Costello (3) passes in the first half against Texas Christian in the Valero Alamo Bowl at the Alamodome in San Antonio, Texas, on Thursday, Dec. 28, 2017. (Rodger Mallison/Fort Worth Star-Telegram/TNS via Getty Images) /

12. K.J. Costello, Stanford Cardinals

Being asked to fill in for Christian McCaffrey was not an easy task. But Bryce Love stepped in and did a phenomenal job. He rushed for over 2,100 yards and nearly 20 touchdowns. He was responsible for more touchdowns than any other Cardinal including their quarterback. He decided to return back to school for his senior season and is an early favorite for the Heisman trophy. For as great as Bryce Love is, he is not the x-factor for the Stanford Cardinals this season. That title belongs to the man giving him the ball K.J. Costello.

In one season as the starter for Stanford, Costello is not going to blow any teams away with his arm. He topped the 200-yard passing mark just twice and once came in a bowl game loss to TCU. The good thing about Costello is he does not turn the ball over. He had just four interceptions last season and two of them came in that TCU game. In an offense led by the ground game, it is understandable that he was not asked to do a lot in the air.

The Pac-12 is open for the taking this year. USC will still be good, the Oregon Ducks are on the rise and Washington seems steady but Stanford is not far off from that pack of teams. It is important for Costello to step up and provide more of a legitimate threat through the air. That will open up the offense and make teams respect the pass. This will open things up for Bryce Love to carve things up on the ground.

Costello does not need to throw for 500 yards a game but even getting his average up to 225 a game would be a major improvement. The challenge will be raising that average and keeping the interceptions down. If the passing yards can jump up, the interceptions stay low and Love stays healthy the Stanford Cardinals could very well make some noise in the Pac-12 this year.