Excess number of balls to knock off (8)
I believe the answer is:
overkill
'excess' is the definition.
(I have seen 'Ridiculous excess ' mean 'overkill' so perhaps 'excess' could also mean 'overkill')
'number of balls to knock off' is the wordplay.
'number of balls' becomes 'over' (cricket term).
'to knock off' becomes 'kill' (knock off can mean to murder).
'over'+'kill'='OVERKILL'
(Other definitions for overkill that I've seen before include "Hyperbole" , "Excessive amount" , "Action far more drastic than necessary" , "Surplus of capacity for task - sounds lethal" , "Ridiculous excess" .)