Snake outside shelter resting (6)
I believe the answer is:
asleep
'resting' is the definition.
(I've seen this in another clue)
'snake outside shelter' is the wordplay.
'snake' becomes 'asp' (asp is a kind of snake).
'outside' indicates putting letters inside.
'shelter' becomes 'lee' (as in lee side, the side sheltered from wind).
'asp' placed around 'lee' is 'ASLEEP'.
(Other definitions for asleep that I've seen before include "coiled up?" , "Snoozing" , "Dormant; inattentive" , "Having forty winks" , "Like kippers" .)