Stretching across a large step (7)
I believe the answer is:
astride
'stretching across' is the definition.
(astride means stretched over or across)
'a large step' is the wordplay.
'large step' becomes 'stride' (I've seen this in another clue).
'a'+'stride'='ASTRIDE'
(Other definitions for astride that I've seen before include "Not side saddle" , "On the back of" , "With feet apart" , "Straddling (horse)" , "Standing over amid tirades" .)