Stifle Red Guards China's No. 2 let loose (8)
I believe the answer is:
throttle
'stifle' is the definition.
(thesaurus)
'red guards china's no 2 let loose' is the wordplay.
'red' becomes 'trot' (Trotskyite, type of socialist or 'red').
'guards' is an insertion indicator (inserted letters are guarded).
'china's no 2' becomes 'h' (2nd letter of 'china').
'loose' indicates anagramming the letters (letters are loosened from their original positions).
'trot' going around 'h' is 'throt'.
'let' is an anagram of 'tle'.
'throt'+'tle'='THROTTLE'
(Other definitions for throttle that I've seen before include "one of the controls in a car" , "Valve regulating volume of fuel and air" , "Check" , "Valve to regulate the supply of fuel to the engine" , "Strangle; fuel controller" .)