Being badly led, sir, they do nothing effective (6)
I believe the answer is:
idlers
'they do nothing effective' is the definition.
The definition suggests an adverb but the answer is not.
'being badly led sir' is the wordplay.
'being badly' is an anagram indicator (letters in the wrong order).
'led'+'sir'='ledsir'
'ledsir' anagrammed gives 'IDLERS'.
Can you help me to learn more?
(Other definitions for idlers that I've seen before include "They hang about doing nothing" , "People who can work but don't" , "The work-shy?" , "Loiterers, layabouts" , "Lazy people, layabouts" .)