Sport scaring hero badly (5-6)
I believe the answer is:
horse-racing
'sport' is the definition.
(horse racing is a kind of sport)
'scaring hero badly' is the wordplay.
'badly' indicates anagramming the letters (letters in the wrong order).
'scaring'+'hero'='scaringhero'
'scaringhero' is an anagram of 'HORSE-RACING'.
(Other definitions for horse-racing that I've seen before include "Sport of kings" , "Riding sport" .)