Heh, I don't know about the law. I've had someone on a skateboard hitch a ride on my car. If you want a safer way to skate head to The Embarcadero, which is the street along the bay. The sidewalk on the bay side is wide, flat, 3 miles long, has no cross traffic/intersections, and you are allowed to skate and bike on it. Also, look out for Sunday Streets events, they close down streets, like all 3 miles of Embarcadero so people get walk, skate, bike, and do whatever they want. http://www.sundaystreetssf.com/

I didn't mention basketball before (SF is more of a baseball town), but the Warriors play in Oakland (across the bay). You can take BART to get there. Unfortunately Aug-Sept is not basketball season, it is baseball season. If you come another time of year you can get tickets on StubHub. I see tickets on there now for as low as $2. http://www.stubhub.com/golden-state-warriors-tickets/

There are public basketball courts if you want to shoot hoops yourself. You can probably find one near where you are staying/working: http://sfrecpark.org/wp-content/uploads/Basketball.pdf