A baseball metaphor (along the lines of getting to the plate, to 1st base, to 2nd base... etceteria) for a member of the opposite sex that obviously desires coitus
but will not make the first move. He/she is just sitting there and all you have to do is "make contact" and the deal is closed i.e. home run.
Those girls so wanted it and were so into us, it was like sex teeball in there.