ballpark vs sports stadium

ballpark and sports stadium both are nouns.

Word	Noun	Adjective	Verb	Adverb
ballpark	Yes	No	No	No
sports stadium	Yes	No	No	No

As nouns, sports stadium is a hypernym of ballpark; that is, sports stadium is a word with a broader meaning than ballpark:

ballpark: a facility in which ball games are played (especially baseball games)
sports stadium: a large structure for open-air sports or entertainments

Other hypernyms of ballpark include arena, bowl, stadium.

ballpark (noun)	sports stadium (noun)
a facility in which ball games are played (especially baseball games)	a large structure for open-air sports or entertainments
near to the scope or range of something