The most common and most likely answer to this crossword clue is the 7 letter word VIVALDI
I've seen this crossword clue in The Sunday Telegraph
V
I
V
A
L
D
I
More clues leading to the result VIVALDI
- He composed line in exam papers the wrong way
- I had smallest room, four, set up for composer
- Composer in short video - one embracing girl
- He managed to score every season
- Seasonal barman in Italy wearing very, very cheap chain
- Composer of the year as represented in pieces
- He composed valid styles for entertaining quartet
- Iliad verses for 5,10
- Composer‘s verses about one supermarket
- For a man of all seasons: best wishes and slow up
Buddy explains!

The straight part
We know that "Composer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case composer = vivaldi.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.