Mocked deer did reform (7)
I believe the answer is:
derided
'mocked' is the definition.
(deriding is a kind of mocking)
'deer did reform' is the wordplay.
'reform' is an anagram indicator (letters in a new form).
'deer'+'did'='deerdid'
'deerdid' is an anagram of 'DERIDED'.
(Other definitions for derided that I've seen before include "Ridiculed" , "Mocked, laughed at" , "Made fun of" , "Scorned" , "Did rubbish" .)