Bit scared after agent oddly disappeared (6)
I believe the answer is:
gnawed
'bit' is the definition.
(gnawing is a kind of biting)
'scared after agent oddly disappeared' is the wordplay.
'scared' becomes 'awed' (awing is a kind of scaring).
'after' says to put letters next to each other.
'oddly disappeared' means one should take alternating letters (letters in odd-numbered positions removed).
The alternate letters of 'agent' are 'gn'.
'awed' after 'gn' is 'GNAWED'.
(Other definitions for gnawed that I've seen before include "Persistently nibbled" , "Chewed at like dog with bone" , "Wore away; champed" , "Bit or chewed persistently" , "Bit persistently at something hard" .)