Caleb Gastelum has provided a feel-good story for Oklahoma in a year plagued with off-the-field problems.

The senior walk-on has overcome the odds to lead the fourth-ranked Sooners in tackles heading into their showdown with Tennessee on Saturday night.

Gastelum, an inside linebacker, matched his entire career total with eight tackles and picked up his first career interception and sack last Saturday against Tulsa. After the game, Coach Bob Stoops announced that Gastelum had been awarded a scholarship.

The locker room went crazy.

"Coach was handing out game balls," Gastelum said. "Then, he paused and said he was handing out a special game ball. He tossed me a game ball and said he was giving me a scholarship, too. It was extremely special for me. Everyone really jumped on me when he said it. It was really special for me."

Gastelum said he believed something good would eventually happen if he stuck with it. He had played in 35 games as a reserve, mostly on special teams, yet he still believed he eventually would have chance to contribute more and gain a scholarship.

"I tell myself every day that hard work pays off," he said. "Sometimes, you get down because you don't think it'll happen and things aren't going your way. You just remind yourself that if you work hard, good things will happen."

The reasons for Gastelum's rise are a combination of his work ethic and others' misfortunes. He entered the season behind last year's leading tackler, Frank Shannon, and Jordan Evans on the depth chart. Oklahoma tried to suspend Shannon after investigating a sexual assault allegation, and while the school waited to see whether it could enforce the suspension, Gastelum moved up on the depth chart.

Early the opener against Louisiana Tech, Oklahoma was already without Shannon when Evans was ejected for targeting. Gastelum played the rest of the way, and his solid performance that night gave him more opportunities against Tulsa. Now that Shannon has been removed from Oklahoma's roster, Gastelum's place as a key component of the defense is secure.

"Obviously, the circumstances aren't the way that we would have liked them to be, but they are what they are, and he has to step up, the next guy up, and play," defensive coordinator Mike Stoops said. "That's always been our philosophy, and our standards won't change, and our expectations won't change for any player."

Mike Stoops said Gastelum deserves credit for staying ready. He said Gastelum studies hard and has a better understanding than ever of Oklahoma's defense.

"I think it takes a special guy to be able to do all that," he said. "It's a hard road. Caleb persevered through a lot of hard times to get himself in position to contribute. That's a credit to him and who he is, to be able to go through all those times and stick it out and you're really getting very little for it."

Gastelum's play in the first two games has drawn Tennessee's attention. The Volunteers see him as a key component of a unit that has allowed averages of just 11.5 points and 286.5 yards in its first two games.

"Very active," Tennessee coach Butch Jones said. "We always talk about, in linebackers, speed, toughness and instincts - STI. He has that. He has a nose for the football. (He's) very, very tough and very, very physical."

Gastelum said he won't change his approach just because he's getting more action. By now, the only way he knows is to push forward and work hard.

"I'm just there for when the coaches need me," he said. "I'll play when they want me to play, and they'll play me when they want me to play. It's all up to them. I just take it upon myself to be ready and be prepared for that situation."

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AP Sports Writer Steve Megargee in Knoxville, Tennessee, contributed to this report.

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Follow Cliff Brunt on Twitter: www.twitter.com/CliffBruntAP .