EUGENE, Ore. (AP) -- Byron Marshall is playing like a starter while De'Anthony Thomas is sidelined with an injury.
Marshall has rushed for more than 100 yards in each of the last four games for No. 2 Oregon, bringing his average to 106.57 yards, good for 21st in the nation. He had 192 yards and three touchdowns in Saturday night's 62-38 victory against Washington State.
There's a simple philosophy behind all these yards for the 5-foot-10 sophomore from San Jose, Calif.
''If you're not getting better, you're getting worse,'' Marshall said after the victory over the Cougars. ''There's no in-between.''
The Ducks (7-0, 4-0 Pac-12) take pride in their ground game, a key component of their speedy spread offense. Oregon is ranked second in the nation with an average of 332.4 yards rushing per game. The Ducks are averaging 643.1 yards overall and 57.6 points.
Marshall has rushed for 759 yards and nine touchdowns on 111 carries. He called his performance against Washington State the best game he's ever had.
Thomas hurt his right ankle on the opening kickoff in Oregon's 55-16 victory over California on Sept. 28, slipping on slick turf from a driving rain. He's missed three games since then, although he has suited up for each one.
Thomas, a versatile back who also runs track for the Ducks, had 338 yards rushing and six touchdowns in Oregon's first three games this season.
Thomas told Oregon's website, GoDucks.com, he expects to return next week against No. 12 UCLA. The Bruins (5-1, 2-1) lost 24-10 at Stanford on Saturday.
''He's a huge playmaker,'' Marshall said, ''and whenever he's not on the field, I think everyone feels like they need to step up.''
If Thomas' absence has shown anything, it's the amount of depth and talent among Oregon's running backs.
The Ducks also are receiving production from true freshman Thomas Tyner, who had a career-best 99 yards rushing and two touchdowns against Washington State - including a 66-yard score in the second quarter.
Tyner has run for 386 yards and seven touchdowns this season. He scored on his first-ever carry as a Duck in Oregon's 59-10 victory over Virginia.
Together, Marshall and Tyner have averaged 207 yards while Thomas has been out. They've scored 11 touchdowns.
''We want to get De'Anthony back as soon as possible, but obviously those guys have carried the load and we feel good about that,'' running backs coach Gary Campbell said. ''We have a couple of extra backs that we can plug in and still get good results.''
Marshall had scoring runs of 1, 26 and 30 yards against Cougars. He said he's feeling stronger with each outing.
''My mentality hasn't really changed that much. I have always had the mindset that once I get on the field I have to dominate the way I know how to,'' he said. ''So now that I am on the field more I just get more of an opportunity to dominate.''
If Marshall has one issue, it's ball security. He fumbled after a 35-yard catch in the second quarter against the Cougars. It was one of two receptions he had in the game. He also fumbled on his first two carries against California, but they came in a downpour that impacted both teams.
''That's definitely a concentration issue,'' Marshall said Saturday night. ''That's no one's fault but my own.''
His focus, for now, is on progress.
''I think the running game has improved, I think we've gotten better every week,'' he said. ''When we get De'Anthony back, we'll be all the better.''