Sports For Nerds: Gridiron Football, Part 1

In my original post, I covered some of the reasons why everyone should have a basic understanding of sports and introduced the first sport I’m to cover: gridiron football, using the American rules.¹

In this post, I’ll cover some of the basics of the game: the field, the ball, the number of players per team, and the procedure of the game. However, first we need to define some units, for non-imperial readers:

• 1 yard = 3 feet = 36 inches = 0.9144 meters
• 1 lb = 16 oz = 0.454 kg

Those should be the only relevant units through the entire series—if I find that others are useful, I’ll introduce definitions then.

The Field

A football field is 120 yards long by 53.3 yards wide. 100 yards of the length are taken up by the field of play, with a 10 yard end zone at each end. The end zones are the goal areas—in order to score a touchdown, an offensive player must reach the opposing team’s end zone.

A set of goal posts rises from the end of each end zone. The goal posts are 18 feet, 6 inches wide, and extend 35 feet² in the air above their 10 foot high gooseneck mount—field goal tries and point-after attempts following a touchdown must pass through these posts in order to score points.

The field surface is generally composed of either natural grass or artificial surface, depending on what a particular team wants. Currently, of 31 stadiums in use³, 14 use artificial surfaces, and 17 use natural grass.

The Ball

The ball is a prolate spheroid⁴, 11 to 11.5 inches in length, 28 to 28.5 inches in circumference around the middle of the ball, and 20.75 to 21.25 inches in circumference around the pointed ends. It weighs 14-15 ounces, and is inflated to an internal pressure between 12.5 and 13.5 pounds per square inch, gauge.

The ball is made of 4 panels of cow hide leather, and is tanned brown. Along one seam, laces are inserted in order to provide a grip for holding and throwing the ball.

Game Length

The game consists of 4 quarters of 15 minutes apiece. Each team has 3 timeouts per half. After 2 quarters, there is a 12 minute halftime period. Teams have 40 seconds to execute a play (this is known as the “play clock”), and the game clock generally continues to run contemporaneously with the play clock. However, there are many occasions that stop the game clock: incomplete passes, players out of bounds, certain fouls, etc. We’ll cover these in more detail as they come up in their respective sections.

The Players

Each team normally has 53 players on their day-to-day roster. Players are platooned into offense, defense, and special teams (kicking and kick returning units). In the early days of gridiron football, players often played both ways (offense and defense), but with the advent of player safety rules, this practice fell out of favor, except when necessary due to injury.⁵ Teams are required to choose 7 players to be inactive for every game, bringing teams down to 46 players to be dressed for game days.

Teams may allocate their players as they wish—we’ll cover the typical distribution of players according to position once we cover the positions themselves—not all positions are needed in equal depth.

Despite 46 players being active for any given game, only 11 may be on the field at any time, in any phase of the game. Having more than 11 (even by accident), is a penalty; when on the defense, it advances the offense 5 yards, and when on the offense, it sets them back 5 yards.

Game Procedure

The actual procedure of an NFL game is complex. This section easily doubles the length of all of the others—and that’s without getting into procedural complications like penalties, onside kicks, fake kicks, etc. We’ll cover all of those in due time—first, we need to establish the basics.

Each game starts with a coin toss. The visiting captain calls the toss as it is in the air, and the winner of the toss gets to choose one of the following:

1. Receive or kick
2. Which goal to defend
3. To defer the choice to the second half

The loser of the coin toss gets to make the other choice. Immediately before the start of the second half, each team’s captains must inform the referee of their choices for the second half. The loser of the coin toss gets the first choice, unless the winner elected to defer the choice.

An example may be illustrative. If the coin is tossed, and I win it, I may choose one of the following:

1. To receive the opening kickoff
2. To kick the opening kickoff
3. Which goal I would like to defend
4. To defer the choice to the 2nd half

In the event I choose 4, I simply choose first at the beginning of the 2nd half, rather than the loser choosing first. In the event I choose 3, the loser of the coin toss chooses whether to receive or kick. In the event I choose 1 or 2, the loser of the coin toss chooses which goal they will defend.

After the coin toss, the team which is kicking off first (which team this is depends on the result of the coin toss!) will kick off, and the game will begin. The kick is off a kicking tee, from the team’s own 35 yard line— 10 players surround the kicker, and run down the field as the ball is aloft to “cover” the kick. They may not cross the line of the ball until it is kicked— doing so is a 5 yard penalty⁶ and causes a re-kick. Kickoffs are also not permitted to go out of bounds—an out of bounds kickoff causes the opposing team to automatically be given the ball 30 yards from the spot of the kick⁷.

The team receiving the kick can either choose to attempt to return it⁸, or let the kick go out of the end zone for what is known as a touchback, in which case, they will start play from their own 20 yard line. The game clock will start as soon as the player exits their endzone.

After the kick return, play proceeds as follows: each team has 4 “downs” (attempts) to move the ball 10 yards downfield. Every time they are able to do so, the downs counter resets back to 1, and they are given another 4 attempts. If they are unable to “convert” after 4 attempts, this is known as a turnover on downs, and possession of the ball reverts to the defense. Thus, most teams will not attempt all 4 downs, choosing either a field goal try or a punt after the 3rd attempt, depending on their position on the field (more on this in the special teams and coaching sections).

If a team elects to punt, a designated punter will punt the ball to the opposing team, who may choose to return the punt⁹, elect to take the field position wherever the punt lands (a fair catch), or let it bounce, which can result in a good/bad bounce (toward or away from your goal), the punt going out of bounds¹⁰, or a touchback. Muffed¹¹ punts can also occur, but their results are subject to a high degree of randomness, and we’ll cover them more in-depth in the special teams posts.

If a team is able to score via a touchdown, they are awarded 6 points, and may choose either an extra point try from the 15 yard line¹² for 1 additional point, or may choose to run another play from the 2 yard line, good for 2 additional points if they are able to make it into the end zone. If a team is able to score via a field goal try, they are awarded 3 points, with no possibility for extra points after the try.

Regardless of how a team scores, if they are able to score, the game repeats, starting with the kickoff phase again, following all of the same rules as before. The two teams thus go back and forth until the quarter ends, at which point they switch sides for the next quarter.

After 4 quarters are in the books, the team with more points is declared the victor. In the event of a tie, the rules are as follows: during the regular season, 1 additional 15 minute quarter is played, with a semi-sudden death format. Both teams are guaranteed at least one possession during overtime, unless the team which possesses the ball first scores a touchdown, in which case, they win the game. After each team has possessed the ball once, overtime shifts to a true sudden death format: any points scored by either team will end the game. If after the 15 minute period, neither team has scored, the game is declared a tie. Playoff rules deviate only in that an infinite number of overtime periods may be played. Initial possession of the football in overtime is determined with another coin toss, like the game-opening one.

Conclusion

That should, more or less adequately, cover the very basics of an NFL football game. The field size, players, ball, and game length are more or less set, with only minor effects on the game length possible via penalties and other in-game occurrences. The procedure of the game is much more fungible—penalties and turnovers regularly have a massive effect on the down & distance changes between plays. I’ll cover these more in the next few posts, as I break down the 3 phases of the game (offense, defense, and special teams) more. As usual, feel free to reach out to me on Twitter with feedback/requests for clarification/etc.

1. Canadian rules exist, but they differ significantly in key areas of the game. ↩

2. This was 30 feet, until a recently adopted rule change, originally proposed by Bill Belichick of the New England Patriots following a controversial loss to the Baltimore Ravens in 2012. ↩

3. The New York Jets and New York Giants share a stadium, MetLife Stadium, in East Rutherford, New Jersey. ↩

4. An egg. ↩

5. The last full-time two-way player in the NFL was “Concrete” Chuck Bednarik, who played center on offense, and linebacker on defense. Bednarik was known as a ferocious tackler, and retired in 1962, after a 13 year career with the Philadelphia Eagles. ↩

6. For example, the kick moves from the 35 to the 30. ↩

7. A kick from the 35 yard line would then be placed on the opposing 35 yard line. ↩

8. In this case, a designated “kick returner” will catch the kicked ball and attempt to run toward the goal with it. ↩

9. Much like with kickoffs, a “punt returner” will catch the punted ball and attempt to run toward the goal with it. ↩

10. An out of bounds punt grants field position wherever it went out of bounds to the team that was on defense. ↩

11. Dropped, or otherwise incorrectly handled. ↩

12. This is essentially a 33 yard field goal try. The rule previously was to attempt extra points from the 2 yard line, a 20 yard kick. This was changed for the 2015-2016 season to make the extra point try not an automatic conversion. At the time of writing, we’ve seen more missed extra point attempts in 7 weeks of the season this year than we saw in all 17 of last season. The rule is clearly working. ↩