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' with letters rearranged gives 'PACES'.
(Other definitions for paces that I've seen before include "Single steps" , "Steps or strides" , "Space for steps" .)