Nothing in a game plan had structured beginning and end (5,3,5)
I believe the answer is:
alpha and omega
'beginning and end' is the definition.
(I've seen this before)
'nothing in a game plan had structured' is the wordplay.
'nothing in' becomes 'o' (I've seen this in other clues).
'structured' indicates anagramming the letters.
'o'+'a'+'game'+'plan'+'had'='oagameplanhad'
'oagameplanhad' anagrammed gives 'ALPHA AND OMEGA'.
(Other definitions for alpha and omega that I've seen before include "In another language, vowels" , "The beginning and end (of the matter)" , "Extremist characters in Athens" , "used to describe the deity" , "identifying with God?" .)