Former usu def as "a no-nonsense attitude in business or politics", but I can't find much support for the latter as a slang expr. Why do you suppose not...

why do you think it should have?

(that's a slow-pitch lob..)

Intuition

Bakersfield republican Bill Thomas...would retire next January....saying he wanted to retire while he still had his fastball--McClatchy Newspapers circa March 7

This was the first instance I had encountered the term used in this metaphoric way and hence I wonder if anyone else has heard this or a similar usage

Apples and oranges.

Hardball (i.e. baseball) is a different (but very similar) game than softball. To play hardball in the metaphorical sense probably gets its name from the fact that it hurts a lot more to get by a baseball and that a baseball can be thrown harder and faster than a softball.

I take "to quit while he's still got his fastball" to mean that he is going to quit while he's at the top of his game, or in his prime. For most major league baseball pitchers (and fast-pitch softball pitchers), the ability to throw a really fast fastball declines with age. (There have been some pitchers with long careers, however, like Nolan Ryan, who played 27 years and threw very fast fastballs into his forties).

good explanation Alex, thanks.