Stay at home after mare runs wild (6)
I believe the answer is:
remain
'stay' is the definition.
('remain' can be a synonym of 'stay')
'home after mare runs wild' is the wordplay.
'home' becomes 'in' ('he's home' can mean 'he's in').
'after' is a charade indicator (letters next to each other).
'runs wild' is an anagram indicator.
'mare' anagrammed gives 'rema'.
'in' after 'rema' is 'REMAIN'.
'at' is the link.
(Other definitions for remain that I've seen before include "Stay (in a place)" , "Airmen (anag.)" , "Stay around" , "Stay (in position)" , "Marine (anag)" .)