Photo of unexpected attempt on goal (8)
I believe the answer is:
snapshot
'photo' is the definition.
(I know that snapshot is a type of photo)
'unexpected attempt on goal' is the wordplay.
'unexpected' becomes 'snap' (I've seen this before).
'attempt on goal' becomes 'shot' (I've seen this in another clue).
'snap'+'shot'='SNAPSHOT'
'of' acts as a link.
(Other definitions for snapshot that I've seen before include "Quick photograph" , "Picture" , "Informal photograph" , "Quick photo" , "Instant record of an event" .)