Injured Player out for one "Down"

[BktBallRef]

Originally Posted by HLin NC

But what is the definition of a down?

SECTION 7 DOWN – LOSS OF DOWN
ART. 1 . . . A down is action which starts with a legal snap (beginning a
scrimmage down) or when the ball is kicked on a free kick (beginning a free-kick down). A down ends when the ball next becomes dead.

Did we have a legal snap? Yup Did the ball next become dead? Yup
The down occurred. Repeating it is a part of the penalty assessment

Exactly, the down was played. The fact that it has to be replayed does NOT mean the down did not occur. If the down didn't occur, there would be no foul, no penalty, no enforcement, and no replay.