Knocks to the mat
I believe the answer is:
decks
'knocks to the mat' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for decks that I've seen before include "Platforms on a vessel" , "Sets of cards" , "Packs of cards (US)" , "Embellishes" , "Packs of playing cards" .)