ASU back Marion Grice scored against Stanford last week but faces one of the top defenses against the run tonight.

A month before Halloween, it seems odd to discuss “must-wins” in college football, but that is what Arizona State believes it faces tonight against Pac-12 South rival USC at Sun Devil Stadium.

“Definitely,” junior left guard Jamil Douglas said. “To win the South, we have to beat USC.”

The Sun Devils (2-1, 0-1 Pac-12) appear to be at their first crossroads of coach Todd Graham’s second season. With a controversial win over Wisconsin, they established national credibility. With a sloppy loss at Stanford, they might have lost it.

A win over USC (3-1, 0-1) would keep them on the road for the Pac-12 South title. A loss would send them on a detour, making their quest tougher. Perhaps the key against the Trojans: Establishing the run game, something ASU has yet to accomplish. Entering tonight’s contest, the Sun Devils average 108 rushing yards, which rank ninth in the Pac-12.

That noise you hear is USC fans chuckling. Through the season’s first month, no one has run the ball against the Trojans. This has gone somewhat overlooked, mostly because USC’s issues — an inexperienced quarterback, a home loss to Washington State, coach Lane Kiffin’s job security — have trumped its successes.

But under first-year defensive coordinator Clancy Pendergast, the Trojans — running a 5-2 base scheme — have yet to give up more than 300 yards in any game. Perhaps more impressive: No one has rushed for more than 106.

“They’ve struggled on defense the past couple years,” said Mike Bellotti, tonight’s analyst on ESPN2. “A lot of people said, ‘Well, they can’t tackle because they don’t tackle in practice.’ Well, they’re tackling this year. Whether it’s confidence in the defense or just putting kids in position to have success, they just seem to be so much better. They’ve always had great talent, but this season that talent has translated to performance.”

Rushing last season wasn’t a problem for ASU. The Sun Devils averaged 205.4 yards per game, 25th-best in the country and most for the program since 1996. But the success hasn’t transferred to this season, the second in Graham’s run, play-action system. The Sun Devils are averaging just 2.9 yards per carry. Of their 110 rushing attempts, only one — a 22-yard dash from senior Marion Grice — has produced more than 20 yards.

“Obviously, we got to continue to improve,” offensive coordinator Mike Norvell said. “You look at what we’re doing, a lot of it is we’re taking what the defense gives us.” With our offense, there will be times when we might be taking a bubble (screen), a slant or something on the perimeter on a run-play call, and with us, we see that as like an outside sweep.

“But if you look at our yards-per-carry average, that’s not anywhere we need it to be. It’s definitely a work in progress.”

Another factor: Junior quarterback Taylor Kelly has yet to run the ball effectively. Last season, Kelly was a weapon on the ground, averaging nearly 40 rushing yards per game. But through three games this season, he’s averaging just 15.

“Teams are trying to contain him, using a spy as we saw a little last week,’’ Norvell said. “But as long as he’s managing it, I actually like the fact that sometimes he’s sitting in the pocket and driving the football. We’ve gotten some nice completions on that, when maybe last year he would’ve immediately tried to take off. There’s got to be a balance to that, but that’s what makes Taylor special.”

ASU is running on just 43.4 percent of its total plays, which ranks ninth in the Pac-12, ahead of only pass-happy California, Oregon State and Washington State. But Norvell said that’s misleading. Last week, for example, ASU passed 12 times on called run plays, adjustments Kelly made after reading the defense.

But no question, the Sun Devils need to improve. Norvell wants the entire offense — not just the line — to be more physical. Douglas said the Sun Devils are more than capable.

“We’re physical enough, we’re big enough,” he said. “We do it against our defense, and they’re pretty good, so we’ll look forward to doing that (tonight).”