Went into beginning and end of Tchaikovsky score (6)
I believe the answer is:
twenty
'score' is the definition.
('twenty' can be a synonym of 'score')
'went into beginning and end of tchaikovsky' is the wordplay.
'into' indicates putting letters inside.
'beginning and end of' says to hollow out the word (remove centre letters).
'tchaikovsky' with its middle taken out is 'ty'.
'went' placed within 'ty' is 'TWENTY'.
(Other definitions for twenty that I've seen before include "Hundredweights to a ton" , "Cardinal" , "This twice denotes normal vision" , "No. between 5 and 1 on dartboard" , "Number" .)