IPA: //ˈsɒftˌbɔːlər//
KK: /ˈsɔftˌbɔlər/
A person who plays the sport of softball, which is similar to baseball but played with a larger ball on a smaller field.
She is a talented softballer who plays for the local team.
Softballer → It is formed from "soft" (from Old English *softe*, meaning gentle or not hard) and "baller" (from the word "ball" which comes from Old Norse *bollr*, meaning a spherical object, combined with the suffix "-er" meaning a person who). A softballer is a person who plays the sport of softball, which involves a softer ball than traditional baseball.
Think of someone who plays with a 'gentle' ('soft') ball — that's why a 'softballer' is a person who plays softball.