Drunkard periodically shouts (3)
I believe the answer is:
sot
'drunkard' is the definition.
(sot can mean a drunken person)
'periodically shouts' is the wordplay.
'periodically' means one should take alternating letters (letters must be selected 'every so often').
The alternating letters of 'shouts' are 'SOT'.
(Other definitions for sot that I've seen before include "A chronic drinker" , "One's often intoxicated" , "Boozer" , "Habitual drunkard" , "Habitual drinker" .)