Field glasses worn by bad researchers (7)

'researchers' is the definition.
(boffin is a kind of researcher)

'field glasses worn by bad' is the wordplay.
'field glasses' becomes 'bins' (short for binoculars).
'worn by' is an insertion indicator (outside letters are worn by those on the inside).
'bad' becomes 'off' (eg meat that's gone off is bad).
'bins' enclosing 'off' is 'BOFFINS'.