When hail of abuse starts, stop! (4)
I believe the answer is:
whoa
'stop' is the definition.
(I've seen this before)
'when hail of abuse starts' is the wordplay.
'starts' says to take the initial letters.
The first letters of 'when hail of abuse' is 'WHOA'.
(Other definitions for whoa that I've seen before include "Order (horse) to stop" , "Command for horse to slow or stop" , "Instruction to a horse to stop" , "Stop! - steady on!" , "Command to horse to stop or stand still" .)