ruck vs scrunch up

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

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

As verbs, scrunch up is a hypernym of ruck; that is, scrunch up is a word with a broader meaning than ruck:

ruck: become wrinkled or drawn together
scrunch up: make wrinkles or creases on a smooth surface; make a pressed, folded or wrinkled line in; `crisp' is archaic

Other hypernyms of ruck include crease, crinkle, crisp, ruckle, scrunch, wrinkle.

ruck (noun)	scrunch 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)	scrunch up (verb)
become wrinkled or drawn together	make wrinkles or creases on a smooth surface; make a pressed, folded or wrinkled line in; `crisp' is archaic
	sit on one's heels