Out in front (5)
'out in front' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ahead that I've seen before include "In the lead, in advance" , "Forward - in front" , "in van" , "In the vanguard" , "Winning" .)
(Other definitions for leading that I've seen before include "Guiding by going in front" , "Most important; ahead" , "Principal" , "Foremost" , "Main" .)