The most common and most likely answer to this crossword clue is the 6 letter word BRUTES
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More clues leading to the result BRUTES
Buddy explains!

The straight part
We know that "beasts" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case beasts = brutes.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BRUTES mean?
BRUTES noun- An animal seen as being without human reason; a senseless beast.
- A person with the characteristics of an unthinking animal; a coarse or brutal person.
- (Cambridge University slang) One who has not yet matriculated.