Softball was introduced as a World Games sport at the 1981 World Games in Santa Clara and discontinued after the 1985 games in London. It was reintroduced as a women's invitational sport in 2009 in Kaohsiung after it had been removed from the Olympic Games programme, and from 2013 it was again part of the official Program.
References
Softball at the World Games Wikipedia(Text) CC BY-SA