The most common and most likely answer to this crossword clue is the 4 letter word DRUB
I've seen this crossword clue in The Daily Telegraph
D
R
U
B
Buddy explains!

The straight part
We know that "Beat" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case beat = drub.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 DRUB mean?
DRUB noun- Carbonaceous shale; small coal; slate, dross, or rubbish in coal.
- To beat (someone or something) with a stick.
- To defeat someone soundly; to annihilate or crush.
- To forcefully teach something.
- To criticize harshly; to excoriate.