Lad's holding fly that bites little bits (9)
I believe the answer is:
smidgeons
'bits' is the definition.
(I have seen 'tiny bits' mean 'smidgeons' so perhaps 'bits' could also mean 'smidgeons')
'lad's holding fly' is the wordplay.
'lad's' becomes 'son's' (lad can informally mean a young boy).
'holding' indicates putting letters inside.
'fly' becomes 'midge' (I've seen this before).
'sons' enclosing 'midge' is 'SMIDGEONS'.
'that bites little' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for smidgeons that I've seen before include "Informally, very small amounts" , "tiny bits" .)