Lightning run (4)
I believe the answer is:
bolt
I believe this clue is a double definition.
'lightning?' is the first definition.
(I know that bolt is a type of lightning)
'run' is the second definition.
(I know that bolt is a more specific form of the action flee)
(Other definitions for bolt that I've seen before include "Leave suddenly and in a hurry" , "Run away; bar of lock" , "From the blue, it's a great surprise" , "wolf" , "Runner" .)