That beast Bert is wrong to go out of turn! (5)
I believe the answer is:
brute
'that beast' is the definition.
(synonyms)
'bert is wrong to go out of turn' is the wordplay.
I cannot really see how this works, but
'turn' could be 'u' (a 'U-turn' is a kind of turn) and 'u' is found within the answer.
an anagram of 'bert' is 'brte' which is present in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for brute that I've seen before include "Cruel person" , "Caliban" , "Savage person" , "Vicious type" , "One monstrous" .)