Why isn a horse-collar tackle always a foul, even when it happens outside the tackle box?
Horse-collar tackles are legal if the runner does not immediately go down or fumble. InstaRef considers it not “immediate” if the runner does anything else before going down or fumbling, or if his run doesn’t end at the exact same place as the defender’s horse-collar action. (InstaRef also checks whether the horse-collar happens within the tackle box, which is legal as well.) A horse-collar tackle against anyone other than the runner is treated as holding and possibly pass interference.
