drop behind vs fall behind

drop behind and fall behind both are verbs.

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

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

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

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

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