Hound dangerous when one's going for run (5)
I believe the answer is:
harry
'hound' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
(Other definitions for harry that I've seen before include "Male" , "English prince - trouble" , "Ravage - prince" , "Persistently harass" , "Make repeated attacks on, badger" .)