there isn't any rule but people like to generalise.
The time commitment thing has some merit, but I and many people I know can train multiple times a week, maintain a decent standard of our respective sports without it affecting our academic careers, so it's not impossible.

You could argue that professional sports attract those who have no strengths elsewhere, and whole "sporting career is fleeting" thing, but since your average premier league footballer makes more in a week then a professor does in a year, I think that's a bit of a silly argument.
( the mighty badger Aphrodite, on a bar stool, by your side, Tue 24 Apr 2012, 10:01, 1 reply)

Sporting careers are fleeting
Sure, professional athletes can have careers of ten or twenty years, but how many of those are there? The overwhelming majority of those who play sport seriously in childhood have stopped doing so by the time they leave university. Compare, if you like, the number of school, university and adult hockey teams. Probably a 100:10:1 drop out rate, or thereabouts.
(ubergeekian, Wed 25 Apr 2012, 16:19, closed)