Crack marksman still? (8)
I believe the answer is:
snapshot
'still' is the definition.
(I've seen this before)
'crack marksman' is the wordplay.
'crack' becomes 'snap' (synonyms).
'marksman' becomes 'shot' (I've seen this in another clue).
'snap'+'shot'='SNAPSHOT'
(Other definitions for snapshot that I've seen before include "Informal photo" , "still taken quickly" , "Pan hosts over casual photo" , "Bit of camerawork" , "print" .)