Attack cricket side’s mirth without hesitation (9)
I believe the answer is:
onslaught
'attack' is the definition.
(an onslaught is an attack)
'cricket side's mirth without hesitation' is the wordplay.
'cricket side's' becomes 'on's' (cricket term, on or leg side).
'mirth' becomes 'laughter' (mirth is laughter or cheer).
'without' suggests deleting specific letters.
'hesitation' becomes 'er' (sound made while hesitating - um, er).
'laughter' with 'er' taken away is 'laught'.
'ons'+'laught'='ONSLAUGHT'
(Other definitions for onslaught that I've seen before include "Sally" , "Destructive attack" , "Aggressive action" , "Heavy attack" , "Hunt goals (anag) - offensive" .)