This doesn’t seem true.
In 2016, American universities hired about 20,000 tenure-track faculty [1]. Adding up the major pro sports leagues, there are very very generously 10,000 American pro athletes, (i.e. people who don’t have day jobs).
I guess things change if you include all the minor league and farm teams, especially for the MLB.
[1] https://www.insidehighered.com/news/2018/10/12/about-three-q...
Are you joking? A small child literally has a better chance of growing up to become a professional athlete than a tenured research professor!