Kurt Warner announced his retirement Friday, and his Hall of Fame credentials have been a topic of conversation. Everyone is familiar with his career: three Super Bowl appearances, one ring, two MVP awards, and a compelling personal story that inspires grocery stock clerks around the country.
According to Pro-Football-Reference, his career Adjusted Net Yards Per Pass Attempt (net passing efficiency minus 45 yards for each interception and with a 20-yard bonus for each TD pass) is 6.7 ANY/A. That's very, very good, and it puts him in league with the era's best passers. But it's not called the Hall of Efficiency; it's the Hall of Fame.
With that in mind, we turn to Win Probability Added (WPA), a narrative stat uniquely suited for measuring performance in terms of how each play helps a team win or lose. Fame is about a lot of things, but it's primarily about wins, so let's see what WPA has to say.
Is Kurt Warner a Hall of Famer? What Does WPA Say?
Expected Points (EP) and Expected Points Added (EPA) Explained
This post will explain the concepts of Expected Points and Expected Points Added. In future posts when I refer to these stats, I'll link here.
Football is a sport of strategy and decision making. But before we can compare the potential risks and rewards of various options, we need to be able to properly measure the value of possible outcomes.
The value of a football play has traditionally been measured in yards gained. Unfortunately, yards is a flawed measure because not all yards are equal. For example, a 4-yard gain on 3rd down and 3 is much more valuable than a 4-yard gain on 3rd and 8. Any measure of success must consider the down and distance situation.
Field position is also an important consideration. Yards gained near the goal line are tougher to come by and are more valuable than yards gained at midfield. Yards lost near one’s own goal line can be more costly as well.
Super Bowl XLIV Game Probabilities
Super Bowl game probabilities are available now at the nytimes.com Fifth Down. This week I also review the model's accuracy this season and discuss the how the concept of hindsight bias misleads us about our ability to predict future events.
Win Probability Added (WPA) Explained
I’ve begun using some new stats here lately, and I want to take the opportunity to explain them clearly. Readership has been increasing rapidly too, and some readers aren't as familiar with the terms we use around here. This post will serve as a reference each time I use the new stats in the future.
Although it’s been used in baseball sabermetrics for several years now, Win Probability Added (WPA) is a new, or at least rediscovered, concept for football stats. It measures each play in terms of how much it increased or decreased a team’s chances of winning the game.
WPA starts with a Win Probability (WP) model of the game of football. Every situation in a game gives each opponent a particular chance of winning, and a WP model estimates those chances. The model created here at Advanced NFL Stats uses score, time, down, distance, and field position to estimate how likely each team will go on to win the game. For example, at the start of the 2nd quarter, a team down by 7 points with a 2nd down and 5 from their own 25 will win about 36% of the time--in other words a 0.36 WP.
Favre's Interception, Paytons 4th Down, And Overtime Coin Flips
There's a lot to cover in this one. It was the perfect Sunday to unveil the real-time comment section on the live WP graph pages. Unfortunately, it was too perfect. The server was overloaded with an explosion in traffic, and I don't think many people were able to see the graphs.
Let's go in reverse chronological order and start with the overtime. The NFL overtime rules are far too arbitrary. A coin flip gave one team the ball and the other never had a chance to respond. This happens in one third of all overtimes, and this time it happened in one of the biggest, most exciting games in recent memory. You can say, "Well, the Vikings had a chance to make a stop." True. But the Saints defense never had to. Because the Saints managed a field goal, their defense was never even asked to take the field. Their "stop" was automatic. There's a lot more wrong with the way NFL overtime works. You can read about it here (or here).
New Feature: Live Comments for WP Graphs
I'm testing out a great suggestion a reader made a couple weeks ago. (Sorry, can't remember who!) The live Win Probability Graphs now feature comments. You can put in your two cents on coaching decisions, remarkable plays, or ask general questions about how the graphs work. Help me test it out during today's conference championship games.
Jets-Colts comment thread
Vikings-Saints thread
Fumble Rates by Play Type
A lot of analysis of running vs. passing takes into account the added risk of interceptions. Almost all sources of passing stats will include team or player interceptions. But fumbles are more tricky. Stat sites will tell you team fumbles, but they usually won't tell you how many were due to rushes or due to passes.
Unlike interceptions, fumbles can happen on either type of play. But is the risk of a fumble even between runs and passes, or are fumbles more likely to occur on one or the other type of play? Further, what about fumbles lost? Are fumbles more likely to be lost on runs or passes? And how does the sack-fumble factor in?
Run-Pass Balance--A Historical Analysis
I’ve been writing a lot about run-pass balance lately, and part of my theory of why teams are perhaps passing less often than they should has to do with the evolution of the sport. Rule changes over the recent decades have generally favored passing. Changes in pass blocking rules and in pass interference rules have made it easier to pass the ball successfully. Even subtle rule changes such as the definition of possession and “control” may have made receiver fumbles less likely.
Tactics and play selection have been refined over the years to take advantage of the rule changes, but I’m not sure that they’ve completely caught up. Results from several studies, including my own, have suggested that in most situations, passing is more lucrative than running. This imbalance implies that passing should be selected more often. As defenses respond to expect more frequent passing, the payoff for passes will decrease as the payoff for runs increases. Eventually, there is an equilibrium where the payoffs should be equal.
In this post, I’m going to look at very simple historical trends. As you’ll see in the graphs below, there is evidence that the current run-pass balance has not responded fully to recent increases in the payoff of passes. All data come from PFR's very cool league historical pages.