athletics vs onside

athletics is a noun but onside is not a noun.

Word	Noun	Adjective	Verb	Adverb
athletics	Yes	No	No	No
onside	No	Yes	No	No

athletics (noun)	onside (noun)
an active diversion requiring physical exertion and competition
participation in sports events as an extracurricular activity
a contest between athletes

athletics (adjective)	onside (adjective)
	not offside; being within the prescribed area of play