WHERE in SF?
SF State has 18 courts, usually most players have partners, but some pretty good 3.5-4.0 players hit the wall or hang around.
CCSF has at least 10, but pickup there is tougher, as it's on the wrong side of the tracks.
GoldenGatePark is the best, 22 courts, but you gotta pay like $4 to play 1.5 hours. Weekdays 10-5, but if high school tennis season is in, only till 2.
Marina at Buchanan and NorthPt. has 4.5 doubles on most weekends.
Dolores Park also.
JuliusKahn, NorthBeach, AltaPlaza has good 4.0 doubles most weekends.
GoldenGateway, CalClub, and SFTennis&Racket are private, are tennis clubs.
Clarendon has the backboard set about 40' from the baseline