muck up vs fumble

muck up is not a noun while fumble is a noun.

Word	Noun	Adjective	Verb	Adverb
muck up	No	No	Yes	No
fumble	Yes	No	Yes	No

As verbs, muck up and fumble are synonyms defined as:

muck up (noun)	fumble (noun)
	(sports) dropping the ball

muck up (verb)	fumble (verb)
soil with mud, muck, or mire	drop or juggle or fail to play cleanly a grounder
make a mess of, destroy or ruin	feel about uncertainly or blindly
	handle clumsily
	make one's way clumsily or blindly
	make a mess of, destroy or ruin