My dear mother had me when she was 15 years old in 1962. If abortion had been legal then, I'm not sure I would be walking this earth today. I'm not advocating that teen pregnancy is a good thing, just saying that it's not the worst thing in the world.
That being said, I was at the gym working out when I went into labor with my DD. Would I want the owner of the gym to tell me I cannot work out in their gym because I am pregnant?
I think playing softball may be a little more dangerous than that but it should be a personal choice not a committee decision unless someone else has legal liability in the situation.