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Football Therapy, by the numbers

Bill Connelly applies advanced stats to each NFL team to help break down their relative strengths and weaknesses.

Most analysts tend to look at stats one way: to answer questions and make declarative statements. But that sells the numbers short. Instead, stats (and their cousin, advanced stats) can — at their best — tell you the right questions to ask. For example, “Team A was last in the league in yards per game” is so much less interesting than diving into why Team A was so offensively challenged.

The fact that we often don’t use stats to their full potential is at the heart of why coaches have been saying “stats are for losers” for so long. Their stats are not our stats. They don’t care that they’re allowing X passing yards per game, for example — or to the extent that they do, it doesn’t really help them do their jobs.

Lucky for them, we’ve found a way of using numbers that coaches can relate to; stats that break down an NFL team’s relative strengths and weaknesses, and very quickly determine which narratives have basis in fact, and which are a bunch of hooey.

But before we get there, we have to start with Bill Walsh.

Walsh’s fingerprints can be spotted all over football. His short-passing concepts have worked their way into most NFL playbooks, and have significantly influenced everyone from BYU legend LaVell Edwards to Air Raid inventor Hal Mumme at the college level. And his insights are as valid now as they were when he was winning Super Bowls. Which is why our five-category analysis is culled in part from Walsh’s bible of coaching, “Finding the Winning Edge.”

Published a little more than 20 years ago, the book is part coaching memoir, part brain dump of everything the three-time Super Bowl winner could think to share. By using his outline of everything an offense needs to achieve when facing various situational factors, then applying advanced stats to translate his vision in a way that no one else has, we can pretty definitively lay out each team’s strengths and weaknesses from year to year.

The most important factors of the bunch:

  • Normal down and distance in the open field
  • Backed-up situations near the goal line
  • Third downs
  • Different levels of the red zone
  • Blitz situations

For an offense (or defense) to be successful, the game plan has to properly account and prepare for these situations. Here’s how we applied values to those concepts.

Normal down and distance in the open field

Walsh repeatedly stressed the importance of staying in normal downs and distances, and since teams spend most of their time in the open field — which we will define as the part of the field between your 10 and your opponent’s 30 — it is the first layer of the game plan.

Walsh said the goal in a given open-field drive was to get at least one first down, position the offense in third-and-manageable situations, and produce enough big plays that you’re producing a good number of your first downs before you even get to third down. “Statistics demonstrate ... that only 25-35 percent of a team’s first downs are generated on third down conversions,” he said.

To track open-play success, we’re going to use the following categories:

  • Open-field standard downs success rate*
  • Percentage of first downs generated on first or second down in open field
  • Open-field big-play rate (i.e. gains of 20 or more yards)
  • Average third-down distance in open field
  • Open-field third-down success rate

* Success rate is a key metric for almost everything I do. I define every play as a success based on down and distance — if you get 50 percent of necessary yardage on first down, 70 percent on second down, or 100 percent on third or fourth down, it’s a successful play — and accordingly, success rate becomes an on-base percentage type of measure for football.

Backed Up Situations Near the Goal Line

Teams aren’t often backed up near the goal line, but it’s such a dangerous area that Walsh felt you should game plan specifically for it. The goals are less ambitious and more conservative: move the ball past your 5 to give your punter room for a full run-up, and minimize risk. Turnovers deep in your own end are the most direct route to points in the game of football.

For this, we will define “backed up” as any play on or inside your 10-yard line, on a drive that began on or inside your 10-yard line. (That eliminates third-and-long plays on drives that started at your 20, or something.)

We’ll look at the following:

  • Backed-up success rate
  • Backed-up turnover rate (i.e., percentage of plays that result in turnovers; it better be really, really close to zero)

Third Downs

“Most teams have very specific tendencies with regard to their defensive package and strategy on third down,” Walsh said. Be it in the open field or some other scenario, third downs need to be a completely different portion of the game plan.

Third downs aren’t all created equal, of course. “A statistical analysis of the more successful teams in the NFL reveals the necessity of focusing on getting the offense into a favorable third-down situation (e.g., either third-and-medium or third-and-short),” Walsh noted.

With that in mind, we will track both third-down success and the types of third downs teams created.

  • Percentage of third downs that are third-and-long (i.e. third-and-7 or longer)
  • Percentage of third downs that are third-and-short (i.e. third-and-1)
  • Third-and-long success rate
  • Third-and-medium success rate
  • Third-and-short success rate

Red Zone Levels

Really, you could break a game down into two key components: creating scoring opportunities and converting them. But the challenges of a given scoring opportunity morph and change as you get closer to the goal line. So do an offense’s prime directives.

Walsh said you should “group your play-calling with regard to the 10-yard divisions of the red zone” — the goal line to the 10, the 10 to the 20, the 20 to the 30. Within each group, play-calling philosophy changes. From the 20 to the 30, you have to be mindful of taking sacks and falling out of field goal range, but inside the 20, you can open things up a bit.

Then things get really complicated near the goal line, according to Walsh:

A first-and-goal offensive package should include two or three runs and one or two passes off of those formations. Don’t hesitate to give serious consideration to throwing the ball on the goal line, particularly from awkward situations (e.g., 1st-and-goal from the 9-yard line, 2nd-and-goal from the 7-yard line, etc.).

Walsh also noted that, since every yard counts, you need to define how much yardage you expect to gain with a given play. That means that you should have a different set of plays to call at, say, the 1 or the 3.

Walsh provides a fascinating amount of detail here, which means we need a few different categories to dig into red-zone effectiveness.

  • Success rate between opponent’s 21 and 30-yard line
  • Success rate between opponent’s 11 and 20-yard line
  • Success rate at or inside the opponent’s 10
  • Turnover rate at or inside the opponent’s 10
  • First-and-goal success rate
  • Success rate at the opponent’s 1 (i.e. the goal line)

Blitz Situations

For a lot of my work, I break plays into two categories based on down and distance: standard downs, in which the offense can either run or pass, and the defense has to prepare for both; and passing downs, when most offenses are going to have to pass to catch back up to the chains.

Predictably, the blitz rate goes up when the opponent knows you’re going to pass, and Walsh said you need to carry “two or three ‘blitz-beaters’” in the game plan to try to create a big play out of a situation that appears advantageous to the defense. “All factors considered, the best way to discourage a team from blitzing is to ‘hurt it’ and to ‘hurt it big.’”

Walsh reserved a completely different piece of the game plan for when opponents are most likely going to be in blitz situations. Based on the points where run-pass rates tend to shift pass-heavy in the pros, I categorized blitz downs as first-and-18 or more, second-and-14 or more, and third-and-3 or more (if it’s more than third-and-2, NFL teams are passing almost every time). We will then measure these categories:

  • Blitz down success rate
  • Blitz down big-play rate (again, 20 yards or more)
  • Blitz down sack rate

Essentially, how frequently are you beating the defense on blitz downs, how badly are you beating them, and how frequently are they getting to your QB (and therefore beating you)?

In addition to Walsh’s game-planning basics, we’re also going to use some advanced stats to further the conversation. The basics:

Marginal Efficiency

Marginal efficiency starts with success rates as measured above, then adjusts for down, distance, and field position. It is presented as a percentage — if your marginal efficiency is plus-2.0 percent, that means your success rate was two percentage points above expectation based on those factors. You can use this concept to gauge success based on rushing, passing, standard downs, passing downs, and any number of concepts. You can read more about the concept here.

Marginal Explosiveness

Marginal explosiveness does the same thing, only with my Isolated Points Per Play (IsoPPP) measure. IsoPPP measures the magnitude of a team’s successful plays, and marginal explosiveness then adjusts that concept for down, distance, and field position. If your marginal efficiency is, for instance, minus-0.05, that means your successful plays generated 0.05 fewer equivalent points per play than the expectation.

These factors play an obvious role in your explosiveness potential — you can’t break a 70-yard gain from your opponent’s 10, after all.

Five Factors

The Five Factors are, in essence, the building blocks of winning football. If you win the battle in terms of efficiency, explosiveness, field position, finishing drives, and turnovers, you will win. We measure efficiency and explosiveness with the marginal figures referenced above. Here’s how we measure the rest:

  • Field position: average starting field position
  • Finishing drives: points per scoring opportunity (defined as a first down inside the opponent’s 40)
  • Turnovers: expected turnover margin. Since fumble recovery rates tend to regress toward 50 percent over time, it is worthwhile to look at what a team’s turnover margin would have been had it recovered 50 percent of all fumbles — its own fumbles and its opponents’.

These aren’t predictive stats, mind you. Aside from the success rate figures, which are reasonably stable, these stats can change pretty significantly from year to year. But they are wonderfully descriptive, and they can assess a team far better than takes like “they stink at running the football” or something. We have data going back to 2009, and we intend to track teams from week to week during the 2018 season. Enjoy!

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