Throttling, flashing a signal to turn (13)
I believe the answer is:
strangulation
'throttling' is the definition.
(I know that throttling can be written as strangulation)
'flashing a signal to turn' is the wordplay.
'flashing' indicates anagramming the letters (flash can mean to move around).
'a'+'signal'+'to'+'turn'='asignaltoturn'
'asignaltoturn' is an anagram of 'STRANGULATION'.
(Other definitions for strangulation that I've seen before include "The choking off of a blood vessel" , "murder" , "The choking off of a flow" , "Act of choking" , "Process of choking" .)