Ultimately back the game plan as shrewd (4)
I believe the answer is:
keen
'shrewd' is the definition.
(I've seen this in another clue)
'ultimately back the game plan' is the wordplay.
'ultimately' says to take the final letters.
The final letters of 'back the game plan' are 'KEEN'.
'as' acts as a link.
(Other definitions for keen that I've seen before include "Fierce - sharp" , "Longing" , "Eager - to lament the dead" , "Anxious" , "Sharp - avid" .)