One playing on their own is totally damned, I admitted (7)
I believe the answer is:
soloist
'one playing on their own' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'totally damned i admitted' is the wordplay.
'totally' becomes 'so' (I can't explain this - if you can you should believe this answer much more).
'damned' becomes 'lost' (similar in meaning).
'admitted' means one lot of letters goes inside another (inserted letters are let in or admitted).
'lost' going around 'i' is 'loist'.
'so'+'loist'='SOLOIST'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for soloist that I've seen before include "Only one playing" , "Lone performer" , "Individual performer" , "this one's on his own" , "musician at front of stage?" .)