Baseball symbolism is not just about the bases. Pitching and Catching are accepted sexual terms too. And “striking out” is an all too commonly used term, as well.
The game is nothing but sexual innuendo:
backdoor slider, bag, ball, caught looking, chin music, choke up, dish, donut, fair territory, force out, gap, high and tight, moon shot, mound, rubber, squeeze, sweet spot, switch hitter
… double header, double play, triple play, rushing the mound …
23rd century Russians still reference baseball.
Vir: There were other women, but I never got past one.
Ivanova: You mean first base.
Vir: No, no, I mean one. You see, we have six a … we have six, you see, and each one is a different level of intimacy and pleasure. So, you know, first you have one, and that’s naa-naa. Then there’s two … and by the time you get to five it’s …
Ivanova: Interrupting Vir, I got it, I got it. I got it. I got it. I don’t know what to tell you, Vir. I’ve never really gotten this whole relationship thing down myself so I’m the last person in the world who should be giving advice on … this sort of thing. All I can say is that enthusiasm, sincerity, genuine compassion, and humor can carry you through any … lack of … prior experience with … high numerical value.
Vir: Wow, I’m gonna remember that. Thank you, thank you.
Ivanova [mouths as he leaves]: SIX!
I honestly don’t think we had any consistent methapors. It was pretty much: Did you fuck her yet, nah just fingered her a bit… we’re a direct lot, us Dutch. We do have about a million verbs that mean fucking though.
I’m sure one of the other Dutch dopers will be here with a whole slur of metaphors I’d totally forgotten.
Sticking your finger in the dyke?
According to Robin Schobosky, a fictional Canadian on How I Met Your Mother, they (ie Canadians) use a hockey analogy (I’m sure Canadians don’t, but the writers love to make Canada jokes through her character.)
According to her, the blue line is kissing, the red line is getting naked, and “in the crease” speaks for itself.
She never said explicitly what in the crease means, but I’d like to think that it’s third base/genital fondling, and actual sex would be a goal.
Your heterosexism is showing here.
The qualification " a member of the opposite sex" is unneeded, ans wrong. Pretty much the same terms are used by GLBT kids also.
What’s second base for gay men?
Also, the baseball innuendo list is noticeably missing the *squeeze *and the suicide squeeze. I’d like to think a ground-ruled double has some meaning as well - like, your partner agreed to a home run, but then her dad showed up.
Isn’t the whole baseball thing something 'merican tv/film writers came up with to circumvent quite puritan rules about what you can and cannot say on TV?
I mean ,when you are bragging to your friends IRL you can be a bit more descriptive than ‘3rd base’, no?
It’s more likely the terms were coined long before game existed. The game of baseball was created to form a context where sexual terminology was accepted as proper language in the Victorian era. Well, not more likely, so much as totally unlikely, but amusing to consider 
Actually I think it is quite likely that the sexual code language developed along with the game. You can be much more descriptive, and explicit, bragging to your friends in some situations. But in ‘mixed company’ or within range of ‘tender ears’, the baseball terms probably replaced existing euphemisms which had grown stale or familiar.
That’s “Robin Scherbatsky” and she’s played by Cobie Smulders, who is, in fact, Canadian.
I have no idea if Canadians actually use hockey analogies IRL, though…
There is the Two Handed Zamboni.
Hockey *penalties *seem more fertile ground for metaphor-reaping. Hooking, slashing, boarding, hand pass, cross-checking, high sticking, spearing…
Does this mean I’m mistaken in my long held assumption that Brits mine their venerated English Tiddlywinks Association’s list of winking terminology for their vulgar sexual conquest euphemisms? I just took it for granted.
Winking Terms (from Wikepedia)
Blitz: an attempt to pot all six winks of a player’s colour early in the game
Bomb: to send a wink at a pile, usually from distance, in the hope of significantly disturbing it
Boondock: to free a squopped wink by sending it a long way away, leaving the squopping wink free in the battle area
Bristol: a shot which moves a pile of two or more winks as a single unit; the shot is played by holding the squidger at a right angle to its normal plane
Carnovsky (US)/Penhaligon (UK): potting a wink from the baseline (i.e., from 3 feet away)
Cracker: a simultaneous knock-off and squop, i.e. a shot which knocks one wink off the top of another while simultaneously squopping it
Crud: a forceful shot whose purpose is to destroy a pile completely
Good shot: named after John Good. The shot consists of playing a flat wink (one not involved in a pile) through a nearby pile with the intent of destroying the pile
Gromp: an attempt to jump a pile onto another wink (usually with the squidger held in a conventional rather than Bristol fashion)
John Lennon memorial shot: a simultaneous boondock and squop
Lunch: to pot a squopped wink (usually belonging to an opponent)
Scrunge (UK): to bounce out of the pot
Squidger: the disc used to shoot a wink[8]
Squop: to play a wink so that it comes to rest above another wink[9]
Sub: to play a wink so that it ends up (unintentionally) under another wink
(these make more sense when one remembers that the British are primarily a nation of fetishists and paraphiliacs). 
This American uses “pulling the goalie” to describe a certain unreliable method of birth control.
Probably true, and I apologize for that. But to be honest, I’m not sure the terminology is actually used by anyone but straight males. Do gay men, or women of any orientation, ever brag (or commiserate) about what base they’ve gotten to?
As to the origin of the metaphor, I imagine it started with “scoring” for having sex. “Did you score with that chick last night?” “No, but I did make it to third base, if you know what I mean.”.
Wiki provides a page on baseball metaphors for sex.
I’ve heard from a (precocious?) 15-year old that the baseball thing was passé, and what to say is what f: French, finger, fellate, fuck. It is less iconic, more abstract, but does make up for it in building a child’s vocabulary (assuming that the etymology of the terms is not lost).
I’m so glad the new GLBT generation is more into sports terminology than when I was younger. We didn’t have pitchers and catchers; we had “active” or “passive” “french” or “greek” . . . which is actually more descriptive, when you think about it.