h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I never played sport professionally but i can possibly offer a few insights into why players (even amatuers) keep playing when they are injured:

They probably don't want someone to take their place in the team (never give a sucker an even break!)

Doctors always overestimate the damage / recovery time ( a common and quite often true theory held by many sportspeople).

It is coming up to finals time, which is why they have been playing / training all year to do ( and besides there is the whole off season to recover).

I once played a rugby grand final after finding out the week before that i had a VERY serious stress fracture in my shin.(the physio had thought i had shin splints for most of the season) I was put on crutches straight away, played the game the next weekend,won, and then was back on crutches for 6 weeks afterwards.

the highest level i ever got to was college intramural softball, where my left knee supposedly bent sideways and backward (but the runner was out at the plate.)
yeah, i kept tryin' to play, too, to be in there for my team. (we won that game and were eliminated in the semifinals the next--i coached 3rd base on crutches.)
now that i'm 47 and often need to wear knee braces, elbow supports and sometimes a wrist brace, i am questioning my own judgement.

The day after i posted that last entry there was an article in the Sydney Morning Herald on pretty much the same topic about Rugby League players (it is finals time here).