Crashing into beast like mule? (9)
I believe the answer is:
obstinate
'like mule?' is the definition.
(mules are famously obstinate creatures)
'crashing into beast' is the wordplay.
'crashing' is an anagram indicator.
'into'+'beast'='intobeast'
'intobeast' anagrammed gives 'OBSTINATE'.
(Other definitions for obstinate that I've seen before include "Stubbornly persistent" , "Firm" , "Stubborn or unyielding" , "Blindly stubborn" , "such as a mule" .)