Choose a pair of pants in a bright team color, then keep the rest of your outfit minimal to let them really stand out. (We love silky track pants like these, which we'd totally wear to the office with a blazer and heels, too.)
For the girl who's a little more goth than cheerleader (or at least more Alexander Wang than Alice + Olivia): opt for varsity jackets and simple sneakers in a classic black and white palette. (Smudgey eyeliner optional.)
You can never go wrong with slim white jeans, a chunky watch and a tank in one of your team colors. (Extra points for a racerback.) But the real winner here is the baseball cap; use that or a beanie to add your second team color only when you want to, so you don't have to walk around in team colors all day. Especially if they're hard-to-pull-off team colors.
the straight leg jean, $165, joe's jeans, shopbop.com; twill ball cap, $49.50, ebbets field flannels, jcrew.com; sleeveless t-shirt, $82, t by alexander wang, thecorner.com; military watch, $150, timex, jcrew.com
This one's especially great when you don't want to wear any team colors but do want to look occasion-appropriate. The mesh details add a subtle touch of athleticism, but not in an aggressive giant-numbers-emblazoned-on-the-back sort of way.