blunder vs drop the ball

blunder is a noun but drop the ball is not a noun.

Word	Noun	Adjective	Verb	Adverb
blunder	Yes	No	Yes	No
drop the ball	No	No	Yes	No

As verbs, blunder and drop the ball are synonyms defined as:

blunder and drop the ball: commit a faux pas or a fault or make a serious mistake

Other synonyms of blunder include boob, goof, sin.

blunder (noun)	drop the ball (noun)
an embarrassing mistake

blunder (verb)	drop the ball (verb)
utter impulsively	commit a faux pas or a fault or make a serious mistake
make one's way clumsily or blindly
commit a faux pas or a fault or make a serious mistake