Run in training overnight (6)
I believe the answer is:
govern
'run' is the definition.
(I've seen this before)
'in training overnight' is the wordplay.
'in' indicates the answer is hidden within the clue.
'GOVERN' can be found hidden inside 'training overnight'.
(Other definitions for govern that I've seen before include "Be in power" , "Rule over or regulate" , "Manage - control" , "'Rule over, control (6)'" , "Exercise authority over a people" .)