"A good ol’ time," "a blast," "a ball" — these are all things that are good to have when the meaning is right. All three phrases just refer to a magnificent time or a lot of fun. Someone who is leaving on vacation, for instance, might be told to "have a ball."
On the surface, one might think that the idiom "have a ball" is referring to a beach ball, baseball or other sports-related ball. It makes sense; after all, if someone has one of these in hand, chances are good that that person is having a good time. Professional ballplayers might literally have a ball and not be having a whole lot of fun because they are working, but for most folks, it seems logical that if someone instructs someone else with this phrase, it’s a metaphor for fun.
In fact, this idiom actually goes back further into history. Balls, or fancy dress affairs, were once the height of the social season in many countries. These high-class affairs were attended mostly by people in the upper class. The finest attire, including top hats, tuxedos, satin or velvet ball gowns and glittering, genuine jewels were common or even expected at these events. The expression "have a ball," which appeared in print as slang in the 1920s, actually refers to these affairs. Initially, though, the phrase “have a ball” carried a slightly sarcastic or ironic tone, as though the well-wisher was qualifying the wish.
This idiom has mellowed and shifted to a gentler position, however. It’s no longer something that must be wished on another person. Now, a person who is reporting on the previous night’s date or a vacation can gush, “I had a real ball!” This is not to say that the phrase has lost its potential for sarcasm, however. A slight change in the tone of voice can let the listener know that last night’s date, while verbally described as having been "a ball," was in fact the furthest thing from it.