Hotheaded fellow, this beast? (4)
I believe the answer is:
hart
'this beast?' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for hart that I've seen before include "Stag" , "providing material for Richard Rodgers?" , "Songwriting partnership, Rodgers and --" , "Deer; Lorenz --, lyricist" , "Beast" .)