Keep going to the Nag’s Head and turning nasty (4)
I believe the answer is:
stay
'keep going' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for stay that I've seen before include "Linger" , "Abide" , "Remain; prop" , "Board; continue" , "Rope or wire used to support a mast" .)