Pitman once bringing in amateur scrutineer (8)
I believe the answer is:
examiner
'scrutineer' is the definition.
(thesaurus)
'pitman once bringing in amateur' is the wordplay.
I cannot really see how this works, but
'pitman' could be 'miner' (I've seen this in another clue) and 'miner' is found in the answer.
'once' could be 'ex' (prefix meaning former or onetime) and 'ex' is found in the answer.
'amateur' could be 'a' and 'a' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for examiner that I've seen before include "Who judges" , "Person testing" , "One administering test" , "One setting a formal test" , "judge" .)