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SECTION 2 - DEAD BALL
ARTICLE 1. DEAD BALL DECLARED
An official shall declare the ball dead and the down ended:
(d)when a runner declares himself down by:
(1)falling to the ground, or kneeling, and clearly making no immediate effort to advance.
つまり自らの意思で倒れて前進しねーよと意思表示すれば、その時点でデッドボールとなり、そのダウンは終了する
QBのニーダウンと同じね
