Yours truly led astray by unknown assortment (6)
I believe the answer is:
medley
'assortment' is the definition.
(I've seen this before)
'yours truly led astray by unknown' is the wordplay.
'yours truly' becomes 'me' (the person that set this crossword).
'astray' indicates anagramming the letters.
'by' says to put letters next to each other.
'unknown' becomes 'y' (algebra).
'led' with letters rearranged gives 'dle'.
'me'+'dle'+'y'='MEDLEY'
(Other definitions for medley that I've seen before include "A linked group of songs or tunes" , "A series of songs in one composition" , "Collection of tunes performed as one piece" , "Miscellany (of pieces of tunes)" , "swimming race" .)