Bat flying in a flap (3)
I believe the answer is:
tab
'flap' is the definition.
(both can mean a small piece of material)
'bat flying' is the wordplay.
'flying' is an anagram indicator (letters fly around into new positions).
'bat' with letters rearranged gives 'TAB'.
'in a' is the link.
(Other definitions for tab that I've seen before include "Running bar bill" , "Till bill" , "Flap; illicit drug pill (slang)" , "Tally at bar (colloq.)" , "ticket" .)