Managed to perform music initially disorganised (6)
I believe the answer is:
random
'disorganised' is the definition.
(I've seen this before)
'managed to perform music initially' is the wordplay.
'managed' becomes 'ran' (both can mean organised or was in charge of).
'to perform' becomes 'do' (both can mean complete an action).
'initially' suggests taking the first letters.
The initial letter of 'music' is 'm'.
'ran'+'do'+'m'='RANDOM'
(Other definitions for random that I've seen before include "Occurring by chance, no fixed pattern" , "Sporadic" , "Happening without method" , "Without order" , "Haphazard, with no particular plan" .)