Reg running back after naughty short-legged omnivore (6)
I believe the answer is:
badger
'omnivore' is the definition.
(I know that badger is a type of omnivore)
'reg running back after naughty short-legged' is the wordplay.
I cannot really see how this works, but
an anagram of 'reg' is 'ger' which is located in the answer.
'naughty' could be 'bad' (badly behaved) and 'bad' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for badger that I've seen before include "Member of the weasel family" , "Beast blamed for TB" , "Nocturnal black and white animal" , "One of the weasel family" , "Torment" .)