ruck vs ruck up

ruck is a noun but ruck up is not a noun.

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

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

Other synonyms of ruck include pucker.

ruck (noun)	ruck up (noun)
a crowd especially of ordinary or undistinguished persons or things
an irregular fold in an otherwise even surface (as in cloth)

ruck (verb)	ruck up (verb)
become wrinkled or drawn together	become wrinkled or drawn together