He started badly, becoming exhausted (9)
I believe the answer is:
shattered
'exhausted' is the definition.
(I've seen this before)
'he started badly' is the wordplay.
'badly' is an anagram indicator.
'he'+'started'='hestarted'
'hestarted' with letters rearranged gives 'SHATTERED'.
'becoming' acts as a link.
(Other definitions for shattered that I've seen before include "Tired; fragmented" , "Broken into bits" , "Broken - exhausted (informal)" , "devastated" , "Splintered" .)