While I understand the impulse to blend in, or to avoid overheating, the trouble with that khaki/polo default setting is you wind up dressed like an intern handing out stat sheets, or one of the clubhouse guys. Worse still, in your cargo shorts and T-shirt you look like you've come to mow the lawn or play in the Chuck E Cheese ball pit. And that's the way you'll be treated. Find a seersucker or linen suit online, brand new, for less than $100.
The point of the dress code is to use common sense. If you don't understand that, you don't belong in this business.
It's been a couple of years since I covered a college game, but I don't think I ever recall seeing one of my fellow sports writers wearing a suit. Khakis and a shirt/tie was about as dressy as it got. Jeans in cooler weather, khaki or decent-looking cargo shorts in warmer weather, sneakers and a polo or button down shirt seemed to be acceptable if not standard. You might be walking a couple of miles over the course of the day, when you factor the walk to and from the car, possibly up some stadium stairs, and around the stadium itself. I always dressed as comfortably as I could while still looking professional.
Dress code depends on whether you have "arrived" in your career. If you're asking here what to wear, I assume this particular game isn't your dream job. But a step up the ladder. When climbing it, dress well. A head coach has probably arrived. He can wear whatever he wants. This is his "house". Look around the press box. Those dressed the most casually have probably reached their comfort zone. Is this where you'd like to spend the next 20 years of your career? If so, wear what they wear. If you'd like more, dress up a little. At our station, we have about six paid interns a year. Always notice the ones who dress up a little because it is a detail. I can send them out on stories easier because they're dressed professionally and can represent well. (As a side note, I dress up for travel/flights and checking into hotels. I found, even as a 19-year-old, I always got better service.)
As a side note, I don't dress up for travel/flights and checking into hotels. I found, I always get great service because both myself and my company pay them a lot of money each year to provide me with good service.
There's a lot of guys wearing linen suits in NCAA press boxes? It's been over 10 years, but I can't remember anyone in NFL press boxes wearing suits. The PR guys were the only ones wearing suits, maybe it's changed.
I haven't covered a college game in two years or a pro game in about a decade. But even in 2006, suits had gone the way of the dodo in the NFL press box. Covered a MNF game between the Packers and Ravens in Baltimore and most were dressed in some combination of dark jeans/nice shoes/sports jackets/button downs. Maybe a sweater. Don't remember anyone wearing a suit.
I never meant to imply that suits were popular in big league press boxes, or even very much present. But I find suits practical - all those pockets for phones and notebooks and so forth - and pretty versatile.