My favorite and by far what i'm best at is men's fast pitch softball, started playing the day after high school baseball ended my senior year. There hasn't been a summer without baseball or softball since tee ball. There are adult summer leagues for baseball, but softball is more fun/convenient...and it's still really competitive, many former college ball players in the league.
I just moved so no longer do this, but used to play basketball at local elementary school 2 nights week as part of the adult education program, usually would get about 8-15 of the same guys each night, it was fun being that the gym was like 75% the size of a regulation court and everyone was athletic and competitive, but nobody's #1 sport was bball.
I've been playing golf since I was 13 and played in high school....it's about time I join a league in the summer.
Wouldn't mind finding a racquetball or horseshoe league to play in.