Up short like a rash knight (7)
I believe the answer is:
hotspur
'knight' is the definition.
(nickname of Henry Percy, 14th-century knight)
'up short like a rash' is the wordplay.
'up short' can be anagrammed to 'HOTSPUR'.
Though, I'm unsure how this is indicated.
Can you help me to learn more?
(Other definitions for hotspur that I've seen before include "Violent and rash chap" , "Sir Henry Percy's name" , "Tottenham ____ FC" , "Impetuous, fiery person - nickname for Henry Percy" , "Percy's name (H.IV Pt.1)" .)