Answer: REARSUP

AnswerCrossword Clue
REARSUPReacts in fear, in a way
REARSUPRises in anger
REARSUPShies violently, as a horse
REARSUPErupts, as in anger
REARSUPShows anger
REARSUPDoes a pesade, in horsemanship.
REARSUPGets on one's high horse?