Beast causing a nasty turn for Reg! (6)
I believe the answer is:
badger
'beast' is the definition.
The definition and answer can be both animals as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'nasty turn for reg' is the wordplay.
I cannot really see how this works, but
'nasty' could be 'bad' (I've seen this in another clue) and 'bad' is found within the answer.
an anagram of 'reg' is 'ger' which is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'causing a' is the link.
Can you help me to learn more?
(Other definitions for badger that I've seen before include "Annoy the burrower persistently" , "A mammal; harry" , "Grab Ed from the animal" , "Pester - nocturnal animal" , "Carnivore - pester" .)