During the late 1970s and early 1980s, several men's professional slow-pitch softball leagues were formed in the United States to build on the growth and talent in the booming men's amateur game during this period.
The American Professional Slow Pitch League (APSPL) was the first such league, lasting from 1977 to 1980. In 1981, it merged with the North American Softball League (NASL), which had played only one season (1980), to then create the United Professional Softball League (UPSL). The merged league competed for two seasons, before disbanding after the 1982 season, ending the pro era of men's softball.
References
Men's professional softball in the United States Wikipedia(Text) CC BY-SA