The most common and most likely answer to this crossword clue is the 7 letter word COARSEN
I've seen this crossword clue in The Daily Telegraph
C
O
A
R
S
E
N
More clues leading to the result COARSEN
- Roughen no cares.
- Fixing one’s car is dull
- Clubs with reason to struggle become rough
- Turn rough when one’s car is wrecked
- Rowers invading Birmingham centre from the east lower tone
- Make more vulgar, getting a censor agitated
- Make more crude, disturbing a censor
- Against including rude word to become more vulgar
Buddy explains!

The straight part
We know that "become rough" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case become rough = coarsen.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 COARSEN mean?
COARSEN verb- To make (more) coarse.
- To become (more) coarse.