Runs with, in shorts (5)
I believe the answer is:
fuses
'runs' is the definition.
(fusing is a kind of running)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for fuses that I've seen before include "Circuit breakers" , "Blends together as with heat" , "Electrical safety devices" , "They interrupt the electric current when they're overloaded" , "Blends or amalgamates, say metals" .)