line of scrimmage vs scrimmage line

line of scrimmage and scrimmage line both are nouns.

Word	Noun	Adjective	Verb	Adverb
line of scrimmage	Yes	No	No	No
scrimmage line	Yes	No	No	No

As nouns, line of scrimmage and scrimmage line are synonyms defined as:

line of scrimmage and scrimmage line: line parallel to the goal lines where football linesmen line up at the start of each play in American football

line of scrimmage (noun)	scrimmage line (noun)
line parallel to the goal lines where football linesmen line up at the start of each play in American football	line parallel to the goal lines where football linesmen line up at the start of each play in American football