Practised moves, ready to join knights, say (3,6)
I believe the answer is:
set pieces
'practised moves' is the definition.
Although both the answer and definition are plural nouns, I cannot see how they can define each other.
'ready to join knights say' is the wordplay.
'ready to' becomes 'set' (synonyms).
'join' says to put letters next to each other.
'knights say' becomes 'pieces' (knight is a kind of piece).
'set'+'pieces'='SET PIECES'
Can you help me to learn more?
(Other definitions for set pieces that I've seen before include "bishops and others?" , "fireworks displays" , "rehearsed moves" , "Well-practised moves" , "men on chess board?" .)