Reason to stay in, maybe (6)
I believe the answer is:
sanity
'reason' is the definition.
(I've seen this before)
'stay in maybe' is the wordplay.
'maybe' is an anagram indicator.
'stay'+'in'='stayin'
'stayin' is an anagram of 'SANITY'.
'to' acts as a link.
(Other definitions for sanity that I've seen before include "Rationality" , "Reason, condition of being compos mentis" , "Soundness of mind" , "Stay in (anag.)" , "Mental health" .)