FBI suspect one of its agents hit (6)
I believe the answer is:
biffed
'its agents hit' is the definition.
I can't tell whether this definition defines the answer.
'fbi suspect one' is the wordplay.
'suspect' is an anagram indicator (a suspicious or unusual spelling).
'one' becomes 'fed' (I am not sure about this - if you are sure you should believe this answer much more).
'fbi' anagrammed gives 'bif'.
'bif'+'fed'='BIFFED'
'of' is the link.
Can you help me to learn more?
(Another definition for biffed that I've seen is " Struck".)