You are going to shout (4)
I believe the answer is:
yell
'shout' is the definition.
(I know that yell is a more specific form of the action shout)
'you are going to' is the wordplay.
'you' becomes 'ye' (historical version of 'you').
'are going to' becomes 'll' (as in he'll, we'll etc).
'ye'+'ll'='YELL'
(Other definitions for yell that I've seen before include "Loud sharp cry" , "Shout - Shetland island" , "roar" , "Call out" , "Shetland isle" .)