I have come to believe that, to shoot professionally and steadily for a large company, being lucky enough to have the right connections is the only thing that's really important. Forget your portfolio; forget actually having any talent. This is why you see crappy photographers as working "professionals".
Sorry for the rant.
(just to counter-balance my rant: yes, I am aware that there are some truly talented and original artists who are working professionals)
I see you put "professionals" in quotes. I would too. The rest of your rant depends on how you define "professional".
If you're talking about someone hired by some throwaway fanzine to cover a game for $30, then you're right, you can see some pretty crappy work. That, however, is a very good way to get credintialed, build up a body of work and, yes, get to know people.
If you define "professional" as someone getting a good rate to make pictures for a mainstream magazine or website, then you're only partially right. Yes, who you know makes a big difference. But you'd better be a hell of a shooter before you even try to get that job. An editor would be foolish to hire his brother in law if his images weren't big league. Especially if he's got a dozen big leaguers applying for every assignment he's got.
If you are applying for that kind of a gig, you'd better be prepared. Editors don't like to have their time wasted, so if you finagle an interview and come in and show crap, he'll remember that. You may not get another chance.
If you want to be a pro sports shooter, you'd better know in your bones that you have to be a sports shooter. If you're the least bit ambivilent about the business or the lifestyle or your ability or the money, then dial back your ambitions. You're competing for too-few jobs against individuals who have no such reservations.