Just ran gleefully, holding throttle (8)
I believe the answer is:
strangle
'throttle' is the definition.
('strangle' can be a synonym of 'throttle')
'just ran gleefully holding' is the wordplay.
'holding' says the answer is hidden in the clue.
'STRANGLE' can be found hidden inside 'just ran gleefully'.
(Other definitions for strangle that I've seen before include "Finish off" , "Subdue" , "Choke to death" , "cut off supply of air" , "Kill by squeezing the throat" .)