Beasts, one incorrectly branded with wrong mark (4)
I believe the answer is:
oxen
'beasts' is the definition.
(I have seen 'Beasts of burden ' mean 'oxen' so perhaps 'beasts' could also mean 'oxen')
'one incorrectly branded with wrong mark' is the wordplay.
'incorrectly' indicates anagramming the letters (I've seen this in other clues).
'branded with' means one lot of letters goes inside another (brand can mean to mark onto or into something).
'wrong mark' becomes 'x' (X is used to show an incorrect answer).
'one' with letters rearranged gives 'oen'.
'oen' placed around 'x' is 'OXEN'.
(Other definitions for oxen that I've seen before include "Steers" , "Horned farm animals" , "Cows and bulls" , "workers in the field?" , "Bulls, buffaloes, etc" .)