For me, in order, I would think it could be any of these:
- Run defense got soft, a la NW averaging wayyyy more on ypc than they should have.
- Fields is uncharacteristically pressured into throwing inaccurately all night and turns the ball over multiple times.
- Corners and safeties (well, really one corner in particular) gets consistently beat over the top for big passing plays.
- Penalties take OSU out of the game.
Again, I think a lot would have to happen for them to drop a game based solely on one of these, but I have definitely had (mild) concerns about all four of these areas at different points throughout the season.