Catapult (9)
'catapult' is the definition.
(I know that catapult can be written as slingshot)
This is the entire clue.
(Other definitions for slingshot that I've seen before include "Catapult -- thin gloss (anag)" , "Weapon American kid may produce" , "fatal to Goliath" , "enough to knock you out" , "No slights (anag) - catapult (US)" .)
(Other definitions for shanghai that I've seen before include "Large Chinese city" , "Port city on the Yangtze estuary" , "Abduct; Chinese port" , "somewhere in China" , "once used to drug sailors, possibly" .)