After 49ers quarterback Brock Purdy broke to the left sideline on a scramble, linebacker Nick Bolton grabbed Purdy's jersey by the name plate. While the pull redirected Purdy, it didn't seem to pull him toward the ground.
Here's the language in the rulebook: "No player shall grab the inside collar of the back or the side of the shoulder pads or jersey, or grab the jersey at the name plate or above, and pull the runner toward the ground."
The key phrase is "toward the ground." A defender can grab a player by the horse collar, as long as the defender doesn't pull him toward the ground.
Here it is. Was Purdy pulled toward the ground? The officials decided it was.