Winter may not be great for weather, but the cold months propel professional football into heavy rotation in living rooms and bars across the country. Take a look at 15 things you might not have realized about the most popular sport on television.

1. IT'S BEEN PLAYED EVERY DAY OF THE WEEK.

While Sunday is pro football’s flagship day and Monday and Thursday nights get in on the action, there have been a handful of pro games played on Tuesdays, Wednesdays, and Fridays, usually as a result of weather delays.

2. OVER A THIRD OF REPLAY REVIEWS ARE OVERTURNED.

There's a good reason coaches challenge official calls by demanding instant replay: they stand at least a one in three chance of having the play overturned.

3. COWS ARE IMPORTANT TO THE GAME.

To make sure that easily gripped “pigskin” is in high supply, equipment makers turn to cows. One cowhide can make roughly 10 footballs. If the balls aren't made of pig leather, why is it still referred to as pigskin? Early players used inflated pig bladders for game balls.

5. QUARTERBACKS CAN HAVE RADIOS.

Originally seen as a method of cheating, radio devices in quarterback helmets allow them to stay in touch with coaching staff during plays. Helmets are expected to get more tech upgrades in the near future, including sensors that can measure the force of an impact so players can leave games to avoid further injury.

6. JERSEYS DIDN'T ALWAYS HAVE NAMES.

In football’s early days, it could be very difficult to identify players. While numbers have always been used, it wasn't until the 1960s that jerseys were produced with the last names of the wearers sewn on.

7. THE HOME TEAM HAS A BALL QUOTA.

While playing in a home stadium has its perks, it does come with some responsibilities: Home teams are expected to have 24 game balls on hand.

8. THE ACTUAL GAME IS PRETTY SHORT.

Television coverage of games can last hours, but the ball can actually be in play for as little as 11 minutes in a given game.

9. THE HUDDLE WAS INVENTED OUT OF NECESSITY.

Players that gather in a tight circle to discuss the next play are a product of a college player who was legally deaf and needed his teammates to pack in closely so he could hear them.

10. THE GAME FOUND AN EARLY HOME IN BASEBALL STADIUMS.

Because baseball was the country’s premiere sport long before football rose to prominence, several pro teams were without home stadiums and were forced to play in major baseball venues—sometimes for decades at a stretch. Today, only one pro team shares its stadium with a baseball squad.

12. THERE ARE SPECIAL BALLS FOR KICKING.

When a punter tees up a ball for a kick, he’s not using a conventional game ball. Known as “K-Balls,” these balls are a little slicker because they’re brand-new, a step that is taken to avoid kickers making any modifications to them. (Some enterprising players used to microwave the footballs to soften the leather.)

13. THOSE ARM BANDS ARE JUST THERE FOR LOOKS.

While some fans may think bicep bands sported by players aren't a fashion statement, they have no practical use. Athletes use them to make their upper arm muscles “pop” more.

14. THERE’S NO TAUNTING.

Players that want to antagonize opponents shouldn't go too far. The pro leagues have rules in place that make verbal taunting a penalty that can be called by officials. Celebratory spiking or spinning of the ball at an opponent is another recipe for a 15-yard penalty.

15. ONLY 500 PEOPLE WATCHED THE FIRST TELEVISED GAME.

Granted, it was in 1939, when few people had televisions. But for a sport that would eventually draw well over a hundred million viewers for its championship games, that’s still a pretty modest start.