My boy has been playing travel soccer (club soccer, whatever) for a fairly competitive club for about a year and a half (he's 9), it definitely hasn't hurt his quickness for baseball etc., which is good because he's pretty small for his age (unlike my DD).
Right now, Soccer is probably his best sport, but he is playing it year round, unlike basketball and baseball.
My DD's secondary sport is volleyball, which I guess may help her hand eye coordination and leg strength a little, but IMHO soccer would make a better second sport for the fall. I'm gonna try to steer my 2 year old towards soccer and softball instead of volleyball and softball
(that's a joke btw, I let them play everything that they can until they get old enough to start choosing their favorites
)
Proud fastpitch, baseball, volleyball, soccer, basketball, etc. Dad