A lot caught in tassel, door swinging up (6)
I believe the answer is:
oodles
'a lot' is the definition.
(oodles means a large amount)
'caught in tassel door swinging up' is the wordplay.
'caught in' indicates the answer is hidden within the clue.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'seldoo' is hidden within 'tassel door swinging'.
'seldoo' in reverse letter order is 'OODLES'.
(Other definitions for oodles that I've seen before include "Large indefinite number" , "Very many, lots" , "a feast" , "Lashings, loads" , "Plenty" .)