just for fun. sports clubs are selective and organized often, and sometimes have people that get involved as a 'coach', but pretty much once you turn 18 and dont play competitively you're not going to ever have a sports coach again.
the more informal sports teams are intermural. theres a bunch of info about them on rec sports' website. they're easy to get into, especially if you have like-minded friends, but you sorta have to stay on top of things to make sure your team is signed up and goes to its games.
i remember i did soccer in the fall and was sorely disappointed because my team only played 4 games the whole semester. you're better off relying on pugs for a more regular fix.
volleyball, tennis, raquetball, and basketball are the most popular impromptu sports on campus not hosted by rec sports.