I want to say that I know how this sort of thing happens. We have a 4 year old daughter. She is very, very choleric. I discipline her a lot. She speaks her mind, isn't afraid of much, including spiders and very tall trees, and is built rather stocky. She is very different from her slim, even spirited older sister.
As such, I can see how easy it would be for her to become interested in all these boy sports, especially if we applauded her successes.
It takes a lot of work in this modern time to help little girls like this become feminine and embrace their womanhood. Some girls are just naturally very girly, while others are not.
In this age of feminism run wild, it's so easy for mothers and fathers to encourage this manish behavior in their daughters. Even more so if the parents have only 2 children where both are girls. I see this a lot, where one girl is allowed to be feminine and sweet and the other girl is encouraged to become heavy and muscular and play sports. It's weird, but happens frequently.