There is a walking/biking path near where I live that I bike on regularly. If it is a warm day, I usually see at least one woman with just a sports bra on top.
Do you ever go on wearing just a sports bra while jogging or walking?
A sports is the closest bra-like thing I wear and I don't do that often. When I do, I always wear a shirt, too. I am fair skinned, burn easily, and often thrash about in bushy, buggy bits. Many of the women I see on my jaunts take a different approach, as suits their needs. To each their own.

I love wearing just a sports bra—it lets my skin breathe, and I know exactly how distracting it is. There is nothing quite like the feeling of working up a deep, hot sweat with nothing but a thin layer of activewear holding me together. It definitely makes the jog a lot more exciting for anyone driving past.