Put down dopiest oddball (7)
I believe the answer is:
deposit
'put down' is the definition.
(I've seen this before)
'dopiest oddball' is the wordplay.
'oddball' indicates an anagram.
'dopiest' with letters rearranged gives 'DEPOSIT'.
(Other definitions for deposit that I've seen before include "Money given as security" , "Put into, bank account say" , "Down-payment" , "Put down - initial payment" , "Put down - leave behind" .)