The most common and most likely answer to this crossword clue is the 7 letter word NASTIER
I've seen this crossword clue in The Guardian
N
A
S
T
I
E
R
More clues leading to the result NASTIER
- Different era isn't more unpleasant
- Degeneration of retinas more unpleasant
- More unpleasant than retsina? Unlikely!
- Close to policeman because row even worse
- Naming and shaming starts and row gets worse
- Closer to breakdown because row is more unpleasant
- Her Maj, after drop of new wine, gets more offensive
- Wine drunk by loveless fiddle player is more disgusting
- Worse bit of hardware, it’s a nightmare to set up
- Education’s ending, as grade not so good
Buddy explains!

The straight part
We know that "worse" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case worse = nastier.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 NASTIER mean?
NASTIER adjective- Dirty, filthy.
- Contemptible, unpleasant (of a person).
- Objectionable, unpleasant (of a thing); repellent, offensive.
- Indecent or offensive; obscene, lewd.
- Spiteful, unkind.
- Awkward, difficult to navigate; dangerous.
- Grave or dangerous (of an accident, illness etc.).
- Formidable, terrific; wicked.