Given the way he bounced around the refs might (MIGHT) have decided he caught the ball in the field of play and went back into the end zone. If he kneels then that’s a safety. It’s really hard to tell on the replays where he caught the ball, but he definitely went backwards voluntarily some time near or after the catch. Getting out of the end zone was the right move then, don’t take a chance on a “further review”.
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That view suggests a certain amount of cynicism WRT the motives of the officials, and I’m not saying that it is unwarranted, but the tendency on the part of the less seasoned members of the secondary to thoughtlessly run the moment the ball hits their fingers has caused many four-and-outs or worse at the goal line.
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