Might one break clay when firing? Or has potter messed up? (4,7)
I believe the answer is:
trap shooter
'might one break clay when firing?' is the definition.
(a trap shooter shoots at clay pigeons)
'or has potter messed up?' is the wordplay.
'messed up?' indicates anagramming the letters (I've seen 'messed up' mean this).
'or'+'has'+'potter'='orhaspotter'
'orhaspotter' with letters rearranged gives 'TRAP SHOOTER'.
(Other definitions for trap shooter that I've seen before include "Sportsman with gun" , "Fellow with rifle" .)