Blunders with insolence on board (5)
I believe the answer is:
slips
'blunders' is the definition.
(I know this)
'with insolence on board' is the wordplay.
'with' means one lot of letters goes inside another.
'insolence' becomes 'lip' (I've seen this in another clue).
'on board' becomes 'ss' (I've seen this in other clues).
'lip' going into 'ss' is 'SLIPS'.
(Other definitions for slips that I've seen before include "errors" , "They try to catch you" .)