Columbia, Mo. ? Whether this is a breakout year for Missouri could depend upon how well the linebackers play in a restructured defense.

The Tigers go into today’s opener at home against Arkansas State with a No. 18 ranking. The offense, led by Heisman Trophy candidate Brad Smith, is expected to be strong.

The question mark is the defense, restructured from a 4-2-5 scheme to a 4-3 base set. The additional linebacker is aimed at slowing the run.

“I think it’s an athletic group of linebackers,” coach Gary Pinkel said. “I think it’s as athletic a group that I’ve probably been associated with in coaching at every place I’ve been.”

The group lacks experience. Senior James Kinney anchors the defense from the weak-side linebacker position, but the other two, sophomores Dedrick Harrington and David Richard, are new to the position.

“Athletically, they’re the mold,” Pinkel said. “You’d clone those guys for the rest of your career. They fit it. But can you play linebacker?”

Harrington moved to middle linebacker from rover, a staple of the 4-2-5. Before, Harrington could move anywhere between the secondary and the defensive line. In his new role, he is pinned in the middle of the defense.

The adjustment simply has taken some time, Harrington said.

“Basically, I’m just closer to the ball,” he said. “I do what any linebacker would do, as far as the scheme. I’ve got to play a lot tougher, a lot harder.”

Richard’s role changed completely. A St. Louis native that began his collegiate career as a tailback at Michigan State in 2002, Richard returned to his home state, sitting out last season due to NCAA transfer rules.

Richard made the switch to defense this spring, though he played the position in high school.

Kinney, an All-American candidate and Butkus Award hopeful, has helped make the transition smoother for Harrington and Richard.

“He’s a person on the field that knows everyone’s responsibilities,” Richard said. “He’s a leader out on the field and a person you love to go to war with.”