(Thanks to Rachel Folowoshele for bringing this to my attention)
John Urschel is a grad student in applied math at MIT. His webpage is here.
Some students go straight from ugrad to grad (I did that.)
Others take a job of some sort and then after a few years go to grad school.
That's what John did; however, his prior job was unusual among applied math grad students
He was in the NFL as a professional football player! See here for more about the career change, though I'll say that the brain-problems that NFL players have (being hit on the head is not a good for your brain) was a major factor for doing this NOW rather than LATER.
How unusual is this? Looking around the web I found lists of smart football players, and lists of football players with advanced degrees (these lists were NOT identical but there was some overlap) but the only other NFL player with a PhD in Math/CS/Applied math was
Frank Ryan- see his wikipedia page here. He got his Phd WHILE playing football. He was a PhD student at Rice.
I suspect that a professional athlete getting a PhD in Math or CS or Applied Math or Physics or... probably most things, is rare. Why is this? NOT because these people are dumber or anything of the sort, but because its HARD to do two things well, especially now that both math and football have gotten more complex. Its the same reason we don't have many Presidents with PhD's (Wilson was the only one) or Presidents who know math (see my post on presidents who knew math: here) or Pope's who are scientists (there was one around 1000 AD, see here).
If you know of any professional athlete who has a PhD in some science or math, please leave a comment on such.
(ADDED LATER- a commenter pointed out Angela Merkel who has a PhD in Physical Chemistry,
is chancellor of Germany, and there is a musical about her, see here.)
(ADDED LATER- some of the comments were for Olympic Athletes and hence not professional and another comment pointed this out. So I clarify: Olympic is fine too, I really meant serious athlete.)