USC coach Lane Kiffin issued a challenge to his defense prior to the scrimmage portion of Thursday’s practice: force two turnovers and the offensive counterparts would be subjected to conditioning drills at the conclusion of the day.

Kneejerk reaction · Sophomore running back Tre Madden injured his knee in Thursday’s practice. The severity of the injury for the former linebacker is not known at this point, though he was taken off on a cart. - Chris Pham | Daily Trojan

Two interceptions later, offensive players lined up for sprints, with one noticeable exception: Sophomore running back Tre Madden, who had exited the field on a cart after sustaining a potentially serious knee injury.

Madden, who recently made the transition from linebacker to running back, appeared to have injured his left knee while making a cut. He was not hit on the play, and the severity of his injury is unknown.

“There’s that concern any time a guy can’t really walk afterwards, so we’ll find out [the details],” Kiffin said.

Most recently, Madden had been heavily utilized in a Wildcat formation. His possible absence is another blow to an already banged-up offensive unit, still slowly bringing a trio of tight ends back into the fold.

“[Freshman] Junior Pomee was out but is expected to practice Saturday,” Kiffin said. “[Sophomore] Randall [Telfer] hurt his hamstring, but [sophomore] Xavier [Grimble] did the most that he’s done since week one, so that was good.”

Although Kiffin took a somber tone regarding a mounting list of injured players, he did have a reason to be optimistic following a strong showing by his defense.

“The defense did a good job today going after the ball,” Kiffin said. “It was good to see them go after it, hopefully they can do that every day.”

One of the defenders who came up with an interception was newly converted linebacker Tony Burnett. Burnett, a senior, entered spring practice as a defensive back and was in just his second day at the new position.

“It’s basically just an extra safety with a little more flexibility to cover slots, so I’ve just got to remain physical like I am,” Burnett said. “[I need to] be a good tackler, and being able to drop into zone coverage is something new for me, but I can do that.”

Burnett’s pick off redshirt freshman quarterback Cody Kessler was Kessler’s first of the spring.

“I was in my zone,” Burnett said. “Basically, I was settled down, reading the eyes of the quarterback, and when he turned his shoulders I broke on the ball and went and got the ball.”

Kiffin said trying Burnett out at linebacker was inspired by redshirt sophomore Dion Bailey’s success at the position along with the departure of Tre Madden as a source of depth after his switch to running back.

“It was really after seeing the success of what Dion has done there — the move from safety to [linebacker] — and moving Tre [Madden], who was the backup there to the offense,” Kiffin said. “We’ll see how it looks for the rest of spring, it looks good so far. He’s fast; he’s actually bigger and stronger than Dion I’d say. Hopefully it can work.”

Whether or not Burnett stays at linebacker long term, he has high hopes for the defensive unit as a whole going into next season.

“We have an offense that can put up 30-40 points a game on any given day, and all we have to do is shut people down and that’ll make the game that much easier because it forces the other team to get in desperate situations,” Burnett said.