Solo Fed agent's guessing game (7)
I believe the answer is:
hangman
'guessing game' is the definition.
(I've seen this in another clue)
'solo fed agent's' is the wordplay.
'solo' becomes 'han' (I can't justify this - if you can you should believe this answer much more).
'fed agent' becomes 'g-man' (I've seen this in another clue).
'han'+'gman'='HANGMAN'
Can you help me to learn more?
(Other definitions for hangman that I've seen before include "Word game - executioner" , "Word-guessing game - executioner" , "Official executioner" , "He suspends" , "Public executioner like Jack Ketch" .)