The Wildcats’ defense needs a big game in the worst way this Saturday against USC. The Arizona football team ranks 112th in the nation in total defense through four games as it has allowed 484 yards per game.

Here are secondary coach Ryan Walters’ three defensive keys to stopping quarterback Matt Barkley, running back Marc Tyler and wide receiver Robert Woods:

“We’ve got to be able to stop the run. They’ve got a good back, good couple of backs, big physical guys. They’ve got a big ol’ line. We’ve got to stop the run.”

Arizona’s giving up 284.7 rushing yards per game in its last three contests, and it doesn’t get any easier with Tyler. The 5-foot-11, 230-pound senior back has 303 rushing yards and two scores through three games. He didn’t play in week one.

“We’ve got to be able defend the play action.”

USC sets up the pass by pounding the ball and hitting defenses with the play action. If Arizona sells out on the run, the Wildcats could get burned by quarterback Matt Barkley, who struggled against ASU last week with two interceptions and a fumble.

“We have to defend the split-zone boots. They do that all day long. I think if you take care of those three aspects of the offense we’ll be all right.”

Barkley does a solid job rolling out of the pocket and finding his receivers so the Wildcats have to stay home and not over-pursue.

— Mike Schmitz