gang up vs gang

gang up is not a noun while gang is a noun.

Word	Noun	Adjective	Verb	Adverb
gang up	No	No	Yes	No
gang	Yes	No	Yes	No

As verbs, gang up and gang are synonyms defined as:

gang up (noun)	gang (noun)
	tool consisting of a combination of implements arranged to work together
	an organized group of workmen
	an association of criminals
	an informal body of friends

gang up (verb)	gang (verb)
act as an organized group	act as an organized group