Shot short geek — he's doomed (5)
I believe the answer is:
goner
'he's doomed' is the definition.
(I've seen this in another clue)
'shot short geek' is the wordplay.
'shot' becomes 'go' (both can mean an attempt).
'short' means to remove the last letter.
'geek' becomes 'nerd' (I've seen this before).
'nerd' with its final letter removed is 'ner'.
'go'+'ner'='GONER'
(Other definitions for goner that I've seen before include "Doomed person" , "One beyond help" , "person about to depart" , "A has-been in distress" , "Someone as good as dead" .)