It's a battle getting piano into small shed (7)
I believe the answer is:
lepanto
'it's a battle' is the definition.
(Battle of Lepanto, 1571 naval battle)
'piano into small shed' is the wordplay.
'piano' becomes 'p' (musical abbreviation).
'into' indicates putting letters inside.
'small shed' becomes 'leanto' (lean-to is an outside building or shed. I am not sure about the 'small' bit.).
'p' going inside 'leanto' is 'LEPANTO'.
'getting' is the link.
Can you help me to learn more?
(Other definitions for lepanto that I've seen before include "Famous 16th-century sea battle; on plate (anagram)" , "Polenta (anag.); battle" .)