Today, I did a track workout, and since it was only going to last about 15 minutes* and all my sports bras that actually fit needed washing, I didn't wear one. And I didn't notice any bounce or discomfort whatsoever. A great discovery!
So from now on, I only need to wear a sports bra if it's warm enough outside to run shirtless (which I do as often as possible, to enjoy feeling the sun on my skin and get a natural source of Vitamin D). And I'm really resentful I need to do it even then, as a woman's nipples really should be legally indistinguishable from a man's. The recent ban on nudity in San Francisco technically only applies to genitalia, but I'm not brave enough to test the waters. I'm very happy to be topless or completely nude around other people who are, in hot tubs and such, but I don't want to be the only woman jogging along the Embarcadero or the Marina wearing nothing above the waist.
* Six laps around a 400-meter track, for the Adult Fitness Test. It actually ended up being 1.6 miles as I was in a middle lane, and I confirmed that I can now sustain 9-minute pace for over a mile!