Since I may be one of the few vol fans that actually chose to watch the ducks play over USCjr and Georgia, I'll put my two cents in on some observations of mine.
1. Don't look at the points they score and think that Oregon physically dominates their opponents like bama, LSU, Georgia, etc. They are an offense COMPLETELY reliant on the big play. The big plays come by the defense being completely out of position and Oregon's speed making them pay. Good gap control will stop the big plays (see Stanford last year where they scored 14 and lost).
2. They suck between the tackles. Anything they get between the tackles is a result of linebackers over compensating and trying to get outside to stop Thomas. Thomas himself can't run between the tackles. He tried a few times against Virginia, once even running into his own blocker and getting blasted. If our corners can funnel Thomas back inside to our linebackers, he won't get outside, and won't hurt you.
3. Down and distance are huge. If you put Oregon in 3rd and long, it makes Mariota a pocket passer, which he is not good at. Guard against the screen, which they like to run on 3rd and long, and you can get them off of the field.
Having said all of this, Oregon is #2 for a reason. They make playing disciplined defense a priority. You don't have to have elite speed to stop them. You have to have a smart defense with good gap control. Virginia was completely out of position several times Saturday, which led to the highlight reel and the lopsided score. Our defense has done a good job of maintaining gap control through the first 2 games. If we have the discipline to do it in Eugene, a lot of people will be shocked at how unimpressive Oregon's offense can look.