Ball game's chaotic conclusion (5)
I believe the answer is:
omega
'conclusion' is the definition.
(omega can mean the end of something)
'ball game's chaotic' is the wordplay.
'ball' becomes 'o' (O looks like a ball).
'chaotic' indicates anagramming the letters.
'game' with letters rearranged gives 'mega'.
'o'+'mega'='OMEGA'
(Other definitions for omega that I've seen before include "Greek character symbolizing resistance" , "character from Athens" , "end of series" , "Final Greek letter" , "Last thing" .)