Loyalist Irishman could go berserk (7)
I believe the answer is:
patriot
'loyalist' is the definition.
(I've seen this before)
'irishman could go berserk' is the wordplay.
I cannot quite see how this works, but
'irishman' could be 'pat' (Patrick is a common Irish name) and 'pat' is present in the answer.
The remaining letters 'riot' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for patriot that I've seen before include "Devotee of their country" , "No traitor" , "A lover of fatherland" , "Chauvinist" , "One who loves his or her country" .)