champion vs plunk for

champion is a noun but plunk for is not a noun.

Word	Noun	Adjective	Verb	Adverb
champion	Yes	Yes	Yes	No
plunk for	No	No	Yes	No

As verbs, plunk for is a hypernym of champion; that is, plunk for is a word with a broader meaning than champion:

Other hypernyms of champion include back, endorse, indorse, plump for, support.

champion (noun)	plunk for (noun)
someone who fights for a cause
someone who has won first place in a competition
a person who backs a politician or a team etc.
someone who is dazzlingly skilled in any field

champion (adjective)	plunk for (adjective)
holding first place in a contest

champion (verb)	plunk for (verb)
protect or fight for as a champion	be behind; approve of