Shuns when without space (6)
I believe the answer is:
avoids
'shuns' is the definition.
(I've seen this before)
'when without space' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'without' means one lot of letters goes inside another ('without' can be similar in meaning to 'outside').
'space' becomes 'void' (void is a kind of space).
'as' going around 'void' is 'AVOIDS'.
(Other definitions for avoids that I've seen before include "Ducks (out of)" , "Shuns, keeps away from" , "Stays away from" , "Keeps away or refrains from" , "Steers clear of, dodges" .)