Reacted like a startled horse and threw (5)
I believe the answer is:
shied
'threw' is the definition.
The definition and answer can be both to do with motion as well as being past participle verbs.
Perhaps there's a link between them I don't understand?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for shied that I've seen before include "horse did this?" , "Flung, tossed" , "Jumped nervously; threw" , "started" , "Thrown" .)