Watch: What the heck is a horse-collar tackle?

This is what the NFL has to say in the rule book.

"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," notes the NFL Football Operations definition, "This does not apply to a runner who is in the tackle box or to a quarterback who is in the pocket. Note: It is not necessary for a player to pull the runner completely to the ground in order for the act to be illegal. If his knees are buckled by the action, it is a foul, even if the runner is not pulled completely to the ground."

The NFL banned horse-collar tackles in 2005, assigning a 15-yard penalty for the offense.  According to nflpenalties.com, the infraction was called 13 times during the regular season. 

Clearly, the rule is open to interpretation as Walker’s hands were placed on the front of Pollard’s shoulder pads. The call helped Dallas score their first points of the game but ultimately had no bearing in a victory for Green Bay

But as teams like the Packers move on in the playoffs, the NFL should offer some clarity on the call