Deceived G-man interrupted by a beefy brute (5)
I believe the answer is:
foxed
'deceived' is the definition.
(foxing is a kind of deceiving)
'g-man interrupted by a beefy brute' is the wordplay.
'g-man' becomes 'fed' (I've seen this in another clue).
'interrupted by' indicates putting letters inside.
'a beefy brute' becomes 'ox' (I can't explain this - if you can you should believe this answer much more).
'fed' enclosing 'ox' is 'FOXED'.
Can you help me to learn more?
(Other definitions for foxed that I've seen before include "Baffled" , "a bit off-colour" , "Deceived in vulpine manner" .)