Performer observed mysterious bloodstains, band disregarded (7)
I believe the answer is:
soloist
'performer' is the definition.
(soloist is a kind of performer)
'mysterious bloodstains band disregarded' is the wordplay.
'mysterious' indicates an anagram.
'disregarded' indicates named letters should be taken away.
'bloodstains' with 'band' removed is 'loostis'.
'loostis' is an anagram of 'SOLOIST'.
'observed' acts as a link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for soloist that I've seen before include "Individual musician" , "musician at front of stage?" , "Lone performer" , "this one's on his own" , "Individual performer" .)