I sing with lads when playing what might be written in score (9)
I believe the answer is:
glissandi
'might be written in score' is the definition.
I can't judge whether this defines the answer.
'i sing with lads when playing' is the wordplay.
'with' says to put letters next to each other.
'when playing' indicates anagramming the letters.
'i'+'sing'='ising'
'ising' put after 'lads' is 'ladsising'.
'ladsising' is an anagram of 'GLISSANDI'.
'what' is the link.
Can you help me to learn more?
(Other definitions for glissandi that I've seen before include "playing, while sliding up and down the passages" , "Series of rapidly ascending or descending musical notes" , "Players may perform them" , "showing smooth actions" , "Slides (music)" .)