An official shall declare the ball dead and the down ended:
when a runner is contacted by an opponent and touches the ground with any part of his body other than his hands or feet. The ball is dead the instant the runner touches the ground. A runner touching the ground with his hands or feet while in the grasp of an opponent may continue to advance; or
Note: If, after contact by an opponent, any part of a runner’s leg above the ankle or any part of his arm above the wrist touches the ground, the runner is down.
2020 Week 4: Indiana @ Chicago
Catch by Roquan Smith - interception or incomplete pass?
A player who makes a catch may advance the ball. A forward pass is complete (by the offense) or intercepted (by the defense) in the field of play, at the sideline, or in the end zone if a player, who is inbounds:
secures control of the ball in his hands or arms prior to the ball touching the ground; and
touches the ground inbounds with both feet or with any part of his body other than his hands; and
after (a) and (b) have been fulfilled, performs any act common to the game (e.g., tuck the ball away, extend it forward, take an additional step, turn upfield, or avoid or ward off an opponent), or he maintains control of the ball long enough to do so.
2020 Week 4: Philadelphia @ San Francisco
Pass to Kendrick Bourne - touchdown or short of the goal-line?