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Learn Football 101 1999–2025 data

How modern footballactually works.

A primer for coaches new to scheme, parents trying to follow a game, and anyone who wants the rest of the Spiral AI library to make more sense. Personnel groupings, how the game has shifted over the last 27 seasons (data pulled directly from nflfastR, 1999-2025), and how to read a defense pre-snap.

Part 01Offense

Personnel, the two-digit code

Every offensive snap has a personnel grouping. The shorthand is two digits: the first is the number of running backs, the second is the number of tight ends. Whatever's left of five eligible receivers (minus the QB) is wide receivers. So “11” is 1 RB, 1 TE, 3 WR. “21” is 2 RB, 1 TE, 2 WR. “13” is 1 RB, 3 TE, 1 WR.

It matters because the defense matches. Three receivers force a fifth defensive back (nickel). Two tight ends keep base personnel on the field. Coaches use personnel to dictate the matchup before the ball is even snapped.

  • 11

    Posse / Eleven

    1 RB · 1 TE · 3 WR

    The modern NFL's base offense. Three receivers force the defense into nickel.

  • 12

    Ace / Twelve

    1 RB · 2 TE · 2 WR

    Two tight ends, heavier, can shift between run and pass without subbing.

  • 13

    Trips TE

    1 RB · 3 TE · 1 WR

    Heavy package, usually short-yardage or goal-line; forces base personnel.

  • 21

    Pro / I-Form

    2 RB · 1 TE · 2 WR

    The old standard. RB + FB for downhill power runs.

  • 22

    Goal-line

    2 RB · 2 TE · 1 WR

    Eight blockers. Almost always run. Modern usage is rare.

  • 10

    Empty (with RB) / Spread

    1 RB · 0 TE · 4 WR

    Four wide. Forces nickel or dime; primarily pass.

Why coaches care

Defenses match personnel by rule (matching the offense's receiver count) and by tendency. If you see 11 personnel jog onto the field, you can usually predict nickel from the defense. If you see 12, you'll see base. The pre-snap personnel chess match decides which scheme has the matchup advantage before a route is run or a block is thrown.

Part 02Passing game

The route tree

Every receiver route descends from one of ten patterns, collectively known as the route tree. They're numbered 0 through 9, with even-numbered routes breaking inside (toward the middle of the field) and odd-numbered routes breaking outside (toward the sideline). Depth generally increases as the number climbs. When you hear a coach call “Z run a 2, X on a 9,” it means slant + go.

This is the common 10-route teaching tree. NFL teams that use Coryell terminology shift some assignments (e.g. 3=Out, 5=Hitch), and Air Raid / Erhardt-Perkins systems use word tags (“Texas,” “Y-Stick,” “Sail”) instead of numbers entirely.

Each diagram shows a receiver lined up on the right side of the formation. The sideline is the white line on the right edge, and the ball sits on the line of scrimmage to the left.

  1. 0Hitch

    5-6 yds deep

    Sprint, stop, face the QB. Quick pitch-and-catch vs soft coverage.

  2. 1Quick Out

    ~5 yds deep

    3-step break to the sideline. Beats off-coverage corners. High-percentage rhythm throw.

  3. 2Slant

    5-6 yds deep

    3-step 45° cut inside. Classic man-beater; against zone, attacks the window between hook defenders.

  4. 3Comeback

    12-15 yds deep

    Push vertical, then snap back down the sideline. Beats off and soft Cover-3 corners.

  5. 4Curl

    10-12 yds deep

    Vertical stem, then sit down facing the QB. Canonical hook/curl-defender beater in Cover 3 and the West Coast curl-flat.

  6. 5Out

    12-15 yds deep

    12-15 yd vertical, then 90° to the sideline. Demands a plus arm; the longest in-air throw in the tree.

  7. 6Dig (In)

    12-15 yds deep

    Square-in across the middle. Sits behind LBs and in front of safeties, eating the Cover-2 hole.

  8. 7Corner

    12-15 yds deep

    Vertical, then 45° to the back-corner pylon. Top Cover-2 beater (high-lows the corner with a flat underneath).

  9. 8Post

    12-18 yds deep

    Vertical, then 45° toward the goalpost. Single-high beater; the skinny variant splits two-deep safeties.

  10. 9Go / Fly

    22+ yds deep

    Straight up the field as fast as you can run it. Takes the top off.

FIG. 1The route tree from a receiver on the right side: outside breaks go right, inside breaks go left. Lines every 5 yards.

Beyond the tree

Modern offenses are built mostly from concepts that stack two or three tree routes together. A handful of patterns live outside the numbered system and show up on every Sunday tape.

  • Drag

    Shallow crosser at 3-5 yards across the field. Mesh staple; finds zone windows and out-runs trailing defenders in man.

  • Wheel

    Out, then up the sideline. Usually run by a RB or slot vs man, leveraging a linebacker matched on a back.

  • Seam

    Vertical up the seam between zone defenders, run by a TE or slot from inside the numbers. Primary Cover-3 stress; also splits Cover 2.

  • Bubble

    Drop-step, then a curved path back toward the QB. Technically the receiver’s route inside a bubble screen play; gets the ball out fast to a slot in space.

  • Whip / Pivot

    Sell the slant, plant, snap back outside. Whip and Pivot are the same route, used interchangeably. Designed man-beater.

  • Mesh

    Two drags crossing at roughly 5 yards under the LBs. Originated at BYU (Edwards and Chow), popularized by Mumme and Leach in the Air Raid, now a staple at every level.

The job matters more

The names matter, but the job matters more. Slants attack the void between man-coverage hips and zone hooks. Posts split safeties. Curls beat soft zone. When you watch a play break open, ask which coverage rule the route just stressed. That's the whole game.

Part 03The data

27 seasons, one graph at a time

Every number below is pulled directly from nflverse-data play-by-play (the data layer behind nflfastR), covering every regular-season offensive snap from 1999 through 2025. Excludes kneels, spikes, and special teams. 34,429 plays in 2025 alone.

The headline shift since 1999

Shotgun adoption

66.1%

2025 · was 12.0% in 1999

Data table
SeasonShotgun rate
199912.0%
200012.9%
200114.0%
200213.9%
200314.3%
200413.2%
200515.6%
200619.5%
200727.0%
200832.3%
200936.9%
201037.8%
201140.5%
201247.5%
201358.9%
201460.8%
201562.5%
201664.3%
201759.5%
201863.8%
201964.7%
202066.1%
202166.1%
202267.8%
202372.2%
202470.5%
202566.1%

The cleanest single-stat story of the modern game. Shotgun went from a fringe formation to the default in under twenty years, peaking at 72.2% in 2023 before settling. Under-center is now the exception.

More stable than the narrative suggests

Pass-vs-run play call

61.0%

2025 pass · was 61.0% in 1999

Data table
SeasonDesigned pass rate
199961.0%
200059.9%
200159.2%
200260.3%
200357.9%
200458.4%
200558.0%
200657.7%
200759.0%
200858.3%
200959.0%
201060.0%
201160.4%
201260.9%
201361.9%
201461.8%
201562.8%
201662.7%
201761.3%
201862.6%
201962.7%
202062.2%
202161.9%
202260.8%
202361.9%
202461.2%
202561.0%

Surprising one. Designed-pass rate (including sacks and scrambles) has lived in a narrow 58-63% band for all 27 seasons. The league isn't passing dramatically more than it did in 1999, it's passing from shotgun. The change is structural, not volumetric.

Rose, plateaued, came back

No-huddle tempo

9.9%

2025 · peaked ~13% in 2014-15

Data table
SeasonNo-huddle rate
19990.0%
20000.0%
20010.0%
20020.1%
20030.9%
20041.1%
20051.6%
20063.6%
20073.7%
20084.0%
20095.1%
20103.8%
20115.6%
20126.7%
201312.2%
201412.6%
201513.2%
201611.5%
20178.8%
20187.6%
20197.9%
20209.4%
202110.8%
202210.4%
20239.2%
202412.2%
20259.9%

Hurry-up offense had its moment in the Chip Kelly / read-option / early Patriots era (~2012-2016), climbing past 12% of snaps. Defenses adapted with substitution tactics and the tempo dropped back toward 9-10% before climbing again recently.

What our trend data doesn't cover (yet)

Personnel groupings (11p, 12p, etc.) and nickel-defense usage require NFL Next Gen Stats data that was only added to the public feed starting around 2016. For context: 11 personnel was about 62% of offensive snaps in 2023 (per NGS via Buffalo Rumblings), and nickel was over 65% of defensive snaps by 2022 (per NFL Football Operations). Those numbers can't be extended back to 1999 cleanly.

Part 04Defense

Reading a defense pre-snap

Before the snap, quarterbacks (and coaches in the booth) look at three things: the safety shell, the box count, and the leverage of the corners. Those three pieces of information narrow the possible coverages down to one or two.

  1. 1

    Safety shell

    How many safeties sit deep.

    1-high
    One safety deep, middle of the field closed (MOFC). Usually Cover 1 (man) or Cover 3 (zone). The middle of the field is guarded.
    2-high
    Two safeties deep, middle of the field open (MOFO). Usually Cover 2, Cover 4, or some pattern-match variant. The middle is exposed but the deep halves are bracketed.
  2. 2

    Box count

    Defenders within ~5 yards of the line of scrimmage.

    6 in the box
    Light. The run is favored.
    7 in the box
    Even matchup.
    8+
    Stacked vs the run. Pass behind it if you can.
  3. 3

    Corner leverage

    Where the corners line up on their receivers.

    Press
    CB on the line, jam at the snap. Tips man coverage or trap techniques.
    Off
    CB 7-9 yards back. Usually zone, and a hitch or quick out is available.
    Inside leverage
    CB tilted inside, giving up the sideline. Bait for an out or fade.

With those three reads, an experienced QB can narrow eight possible coverages down to one or two before the snap. That's what the cadence is buying time for.

Part 05Reference

Glossary

Terms you'll hear repeatedly across the rest of the library.

MIKE
Middle linebacker, the QB of the defense, identifies the protection points.
WILL
Weak-side linebacker, usually the fastest of the three LBs.
SAM
Strong-side linebacker, the one aligned to the TE side.
3-tech
DT on the outside shoulder of the guard. Primary interior pass rusher.
1-tech / NT
DT shaded on the center. Eats blocks, keeps LBs clean.
EMOL
End man on the line of scrimmage. Sets the edge.
RPO
Run-pass option. QB reads one defender post-snap, gives or throws.
Shell
The safety alignment pre-snap (1-high, 2-high, etc.).
MOFO / MOFC
Middle of field open / closed, based on safety count.
Leverage
A defender's alignment relative to a receiver (inside / outside).
Force
The defender responsible for turning a run back inside.
Cutback
A run lane behind the play-side flow when defenders over-pursue.
Combo block
Two OL temporarily double a DL before one climbs to a LB.
Pull
An OL leaves his spot and runs laterally to lead-block.
Crack
An outside-in block by a slot/outside WR on an inside defender.
Arc
An inside-out lead block, usually by a TE or H-back.
Hot route
A pre-snap receiver adjustment to beat a blitz.
Bracket
Two defenders assigned to a single receiver (inside + outside).

Data & sources

All trend data on this page is pulled directly from nflverse-data play-by-play parquets (the data layer behind nflfastR), aggregated via DuckDB and committed to the repo as static JSON. Public sources only, no paywalled data. Last refreshed: May 2026 (covering the 2025 NFL season).

  1. Pass rate, rush rate, shotgun rate, no-huddle rate (1999-2025): nflverse-data PBP releases. Regular-season offensive plays only (kneels, spikes, special teams excluded).
  2. 11 / 12 personnel usage 2023, Next Gen Stats, summarized in Buffalo Rumblings. Personnel data wasn't public in the PBP feed pre-2016, so no 27-year trend.
  3. Nickel usage league-wide (Week 3, 2022): NFL Football Operations.
  4. Route tree numbering, depths, and coverage stress cross-checked against Matt Bowen's NFL 101, the Ravens playbook tree, and the Scouting Academy glossary. Mesh attribution to BYU (Edwards / Chow) per Underdog Dynasty's Air Raid series.

Where to next

Take it to the library.

With the basics down, the rest of the library will read faster.

Offense LibraryDefense LibraryMatchup Lab