Sports are great. Just make sure you stretch beforehand and only play with folks who take safety seriously - it can suck to lose a skiing season because your basketball teammate caused you to roll your ankle.
Stretching happens after if ever, not before :)
From what I know: Stretching after doing a workout is bad, because it tenses muscles even more, stopping the flow of blood in the muscle and thus, making muscles more sore. But maybe that opinion is just the current trend.
on phone, but sources are a quick search away.