Horse in shock couple of rounds - it’s trailing (9)

'horse' is the definition.
(Appaloosa is an example)

'shock couple of rounds it's trailing' is the wordplay.
'shock' becomes 'appal' (synonyms).
'couple of rounds' becomes 'OO' (round can mean a round object like an O).
'it' becomes 'sa' (SA can mean sex appeal, as in 'it').
'trailing' is a charade indicator (letters next to each other).
'appal'+'oo'+'sa'='APPALOOSA'

'in' acts as a link.