Mixon should have took a knee at the half yd line.

[McC]

Physics prevented him from taking a knee. When he came through the hole, he had too much forward lean and momentum to be able to take a knee. And he had to break at tackle at the LOS, which is why he was leaning to begin with. It was only a four yard run with defenders all around.

Taking a knee at the end of a longer run with nobody around is really the only way taking a knee works.