Small three-wheeler beginning to roll forward (7)
I believe the answer is:
striker
'forward' is the definition.
(forward can mean a football striker)
'small three-wheeler beginning to roll' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'three-wheeler' becomes 'trike' (tricycle).
'beginning to' suggests taking the first letters.
The first letter of 'roll' is 'r'.
's'+'trike'+'r'='STRIKER'
(Other definitions for striker that I've seen before include "Industrial activist" , "One expected to score in football" , "One refusing to work - rings the bell" , "refusing to play?" , "Soccer player whose main function is to score goals" .)