Let's see...
If you want to party with bros, go to illegal petes on university. In Tucson they attract a super bro crowd (moreso than anything that you're ever going to find in boulder, at any bar), but they have a lot of outdoor seating, cheap drinks, and a fun atmosphere. It shouldn't be more than 85 degrees during the day... hopefully.
Next door to illegal petes is frog and furkin, which is a slightly more upscale atmosphere, but not by much.
Across the street is gentle ben's, which is going to give you a significantly calmer atmosphere than either of these two places, but it will still be packed and pretty exciting.
These three venues are about a ten minute's walk from the stadium, and right next to campus. This is where the action will be, other than at the frat houses.
If you enjoy drinking beer in a setting where no one is going to give a **** about college football (perhaps friday evening before the game), I highly recommend dragoon brewery for a super low-key experience with outstanding beer, or pueblo vida downtown (also a local brewery with excellent beer) for something probably more exciting, and also much closer to the action. Tap and bottle is an excellent bar with an outstanding collection of beer and a pretty interesting atmosphere, as well, if that's what you're in to.
EDIT: I forgot. A pretty good game day alternative to the bro atmosphere on University is a pizza/beer establishment called 1702. This is probably a 15-20 minute walk from the stadium. They have about 50 taps, and often have some excellent offerings. They serve giant (and I do mean absolutely giant) slices of pizza. If you're looking for something more calm but still fun, this might work, but the downside is that if you get there and it's crowded or you don't like the vibe, you'll have to drive or uber to the next place, because it's not immediately next to any other bars or restaurants that you're likely to be interested in (unless going to some place called dirtbags with a bunch of frat guys tickles your fancy).
PM me if you need more details.