Walks erratically in space (5)
I believe the answer is:
paces
'walks' is the definition.
(pacing is a kind of walking)
'erratically in space' is the wordplay.
'erratically' indicates anagramming the letters.
'space' anagrammed gives 'PACES'.
(Other definitions for paces that I've seen before include "Single steps" , "Steps or strides" , "Space for steps" .)