Against throwing a tin (4)
I believe the answer is:
anti
'against' is the definition.
(prefix meaning against)
'throwing a tin' is the wordplay.
'throwing' indicates an anagram (letters get thrown around).
'a'+'tin'='atin'
'atin' with letters rearranged gives 'ANTI'.
(Other definitions for anti that I've seen before include "not favoured" , "Policy's opponent" , "Definitely not pro" , "Against, informally" , "Naysayer" .)