The most common and most likely answer to this crossword clue is the 6 letter word CELLOS
I've seen this crossword clue in The Sunday Telegraph
C
E
L
L
O
S
Buddy explains!

The straight part
We know that "Instruments" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case instruments = cellos.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 CELLOS mean?
CELLOS noun- A large stringed instrument of the violin family with four strings, tuned from lowest to highest C-G-D-A, and played with a bow, also possessing an endpin to support the instrument's weight.