playing field boundary (competitive karuta)
Refers specifically to the boundary line of the playing field in competitive karuta (a Japanese card game).
If you go out of the playing field boundary, it's a foul.
The players sit inside the playing field boundary.
Compound of 競技 (kyōgi, 'competition') and 線 (sen, 'line'), literally 'competition line'. The term is specific to competitive karuta.