In an episode of Cougar Town, I noticed one of the characters told her friend 'I don't swing at soft balls'. First I thought it was an idiom, but I couldn't find it anywhere when I started looking it up. Here's the dialogue:

> 
> Girl 1 - Luckily, I can control my gag reflex.  
> 
>  Girl 2 - *(ignoring)*  
> 
>  Girl 1 - What, nothing?!  
> 
>  Girl 2 - I don't swing at soft balls.
> 
> 
> 

I would like to know whether this is normally used in English or it is just a phrase coined for the occasion.