It's difficult to pinpoint just one crucial matchup in a game like this where the Buffs are largely outmanned and overmatched across the field. Add to that the uncertainty at the quarterback position and it's hard to say with confidence which unit's play will be most important to staving off demolition and keeping Oregon within reach.
Aside from how well Sefo Liufau is recovering from his first concussion and how well Jordan Gehrke plays if given time the defense is going to be the most critical component to any semblance of hope (Football Study Hall is giving CU a 1.4% chance at victory, Lloyd) the Buffs have at playing this one tight and giving Oregon a scare. Whether or not they're able to slow down Oregon's rushing attack and limit those signature explosive plays will likely be the deciding factor in Eugene on Saturday.
Colorado's Rush Defense vs. Oregon's Ground Game
Oregon boasts what may be one of the most dangerous backfield duos in the country in the combination of sophomore Thomas Tyner and freshman Royce Freeman. Listed at 6'0" and 229 pounds, Freeman is a powerful and bruising yet fast and agile back in the mold of former Oregon great Jonathan Stewart. As the number one option he's adept at cutting through holes and fending off tackles, and if he finds the open field he has the breakaway speed to capitalize. He's rushed for 5.6 yards per carry to this point and has racked up 14 scoring runs. Tyner acts as a speedy, shiftier change of pace back. He's received just under half of the carries that Freeman's been given but has still been effective accumulating 387 yards (essentially what Michael Adkins has produced as CU's leading rusher) and 3 touchdowns.
The Ducks run one of the most effective zone reads in college football and this is in large part due to the fact that they have the most talented player in the nation calling the shots. Marcus Mariota is the entire package, as dangerous with his arm as he is with his feet. When he and his offensive line are fully healthy this Duck offense is as close to an unstoppable force as it gets. However, that hasn't been the case for large portions of this season and Oregon will be without the services of stalwart center Hroniss Grasu for the first time after he suffered a leg injury in Salt Lake City. Mariota will also be missing one of his biggest targets, tight end Pharaoh Brown, who suffered a severe knee injury late in that Utah contest. Brown was a consistent red zone target, with him out I'd expect the Ducks to keep the ball on the ground more often when they're inside the 20 making the play of Colorado's front seven even more important.
According to the S&P+ defensive ratings the Buffaloes rank 101st in the nation at defending the run, while Oregon possesses the 2nd ranked rushing offense. This sets up rather poorly for Colorado, especially when you factor in the Buffs' issues with allowing big gains and the ease with which the Ducks create explosive plays. Even through all of the injuries, CU's safeties stepped up and played well enough to give their team a chance to win two weeks ago in Tucson. That ragtag crew will be called upon again to make touchdown-saving tackles when Oregon's playmakers inevitably reach the second level on Saturday. The secondary as a whole continues to be the relative strength of this defense and they'll play a large role in helping to contain big plays.
Colorado's defensive front has become incrementally better at producing a pass rush this season and they might have a shot at flushing Mariota more than a time or two against a somewhat banged up Duck offensive line. However, even if they do produce pressure and force Mariota out of the pocket when he drops back the Heisman favorite is one of the best in the country at creating on the run and CU has been far from effective at containing mobile quarterbacks who can gash defenses. The Buff linebackers, led again by Addison Gillam who should be able to play a significant amount of snaps on Saturday, will need to pursue smartly and anticipate when Mariota keepers are coming.
This defense does not have the team speed to catch up to loose Oregon ball carriers and will absolutely have to keep everything in front of them. They'll likely bend but if they don't break (i.e. allowing huge explosive gains) they can give their offense chances to match scores with the Ducks and make this a ballgame. That's one large if, however.