On reflection, discerned the heartless ringleader was a ne'er-do-well (6)
I believe the answer is:
waster
'a ne'er-do-well' is the definition.
(both can mean an idle person)
'on reflection discerned the heartless ringleader' is the wordplay.
'on reflection' says the letters should be written in reverse.
'discerned' becomes 'saw' (I've seen this in another clue).
'heartless' means to remove the middle letters.
'ringleader' becomes 'r' (first letter of ring).
'the' with its middle removed is 'te'.
'saw' written backwards gives 'was'.
'was'+'te'+'r'='WASTER'
'was' acts as a link.
(Other definitions for waster that I've seen before include "Squanderer, profligate" , "Prodigal" , "Layabout" , "Person doing nothing of value (colloq.)" , "Useless person, good-for-nothing" .)