Spear dropped on Marx (5)
I believe the answer is:
harpo
'marx' is the definition.
(Harpo Marx)
I don't understand how the remainder of the clue works.
(Other definitions for harpo that I've seen before include "Silent Marx brother" , "one from family of comedians" , "silent film star" , "The dumb Marx brother" , "One of the Marx Brothers" .)