The NFL has changed the rules over time, to better protect quarterbacks and promote a more offensively-oriented game.
rules and regulations
In many Canadian cities, if you try to catch a cab in the dead of winter, after a hockey game, early in the morning after exiting a club, or at peak holiday times, good luck. Most Canadian cities of significant size have regulations that limit the number of taxis. That creates an artificial shortage and plenty of shivering Canadians on sidewalks from coast to coast.