Mostly walking over Hollywood star (6)
I believe the answer is:
pacino
'hollywood star' is the definition.
(I've seen this before)
'mostly walking over' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'walking' becomes 'pacing' (pacing is a kind of walking).
'over' becomes 'o' (cricket abbreviation).
'pacing' with its last letter taken away is 'pacin'.
'pacin'+'o'='PACINO'
(Other definitions for pacino that I've seen before include "Hollywood star" , "Al --, actor" .)