Weapon has a gentle hit in movement (8)
I believe the answer is:
catapult
'weapon' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for catapult that I've seen before include "Child's stone shooter" , "Device with elastic for hurling small stones" , "Slingshot" , "Aircraft carrier launcher" , "Device for firing stones or rocks" .)