Mark Brader:
Mark Brader:
If you go to a baseball game and it's canceled due to weather, you
turn in your ticket stub for compensation in the form of admission
to a future game. ...and is called a raincheck.

Erick Barkhuis:
...which fits very well with the North-American expression "I don't
know exactly, but my ballpark guess would be..."

[referring to spectators, who couldn't really tell whether a runner was
out or not, but at the same time boo the umpire because the call went
against their own guess...]

Ah, sorry, no. It means a guess that you don't expect is right, but you
do know it won't be terribly wrong. It will be "in the right ballpark"
(that's another common expression) -- a ballpark being a fairly large but
still limited area. Ballpark guesses are made on numerical questions,
not questions like whether a runner was out.

I've been googling for a while to see where the phrase "ballpark guess"
comes from, but haven't found a reliable source, yet.

So far, my friends in the States have always confirmed, that "ballpark
guess" comes from the fact that everyone in a ballpark claims to know
what's going on, but in fact merely guesses. This is quite different
from your "a ballpark is a large but still limited space". It might
well be that you're absolutely right (your explanation sounds
plausible)....but on the other hand, how has the ballpark become symbol
for such space and not any other limited space like a concert hall, a
gym, a space shuttle or a transport container?

--
Erick