drop back vs fall back

drop back and fall back both are verbs.

Word	Noun	Adjective	Verb	Adverb
drop back	No	No	Yes	No
fall back	No	No	Yes	No

As verbs, fall back is a hypernym of drop back; that is, fall back is a word with a broader meaning than drop back:

drop back: to lag or linger behind
fall back: hang (back) or fall (behind) in movement, progress, development, etc.

Other hypernyms of drop back include dawdle, fall behind, lag.

drop back (verb)	fall back (verb)
take position in the rear, as in a military formation or in the line of scrimmage in football	go back to bad behavior
to lag or linger behind	retreat
	hang (back) or fall (behind) in movement, progress, development, etc.
	fall backwards and down
	move back and away from
	have recourse to