hang back vs drop behind

hang back and drop behind both are verbs.

Word	Noun	Adjective	Verb	Adverb
hang back	No	No	Yes	No
drop behind	No	No	Yes	No

As verbs, hang back and drop behind are synonyms defined as:

Other synonyms of hang back include drag, drop back, get behind, trail.

hang back (verb)	drop behind (verb)
to lag or linger behind	to lag or linger behind