Posted by Mike on March 5, 2012
Today we're rolling out a new feature -- expected points on boxscores, year pages, and team pages back through 2000. What are expected points, you ask? Inspired by a concept introduced by Bob Carroll, Pete Palmer, & John Thorn in their 1988 book The Hidden Game of Football, our crack staff of statisticians (Sean and Neil) have used a decade's worth of play-by-play data to develop a formula that estimates the expected number of points given a combination of down, distance, and yard line. Let's look at this year's Super Bowl for an example. The first play after the kickoff looks like this:
|1||10||NYG 23||Ahmad Bradshaw right tackle for no gain (tackle by Brandon Spikes)||0||0||0.48||-0.07|
That means that given a first and ten from their own 23, the expected value of the next score in the game is roughly 0.48 points by the Giants. With a run for no gain (resulting in second and ten from their own 23), the play changed that to -0.07 expected points, meaning that the play itself had a value of -0.56 expected points. Looking at the first touchdown of the game, we see:
|2||2||NWE 2||Eli Manning pass complete short middle to Victor Cruz for 2 yards, touchdown||8||0||5.72||7|
|Lawrence Tynes kicks extra point good||9||0||0||0|
Before the play was run, the expected points for a second and goal play from the 2 yard line is 5.72 points, so scoring the touchdown there netted the Giants 1.28 expected points (note that for touchdowns, 7 points are assumed and a made extra point is not worth any additional points, though a missed extra point subtracts one and a made two-point conversion adds one).
What can we do with these? Well, when you sum all of the differences together (minus an adjustment for the end of half and end of game plays), you should get the scoring margin of the game, which you can see in the table below the box score:
|New England Patriots||-4.00||10.70||9.71||0.99||-1.42||-13.35||-15.90||0.22||0.00||-1.47||-3.11||1.71||0.95||0.14||-1.16|
|New York Giants||4.00||13.35||15.90||-0.22||0.00||-10.70||-9.71||-0.99||1.42||1.47||-1.71||3.11||-0.14||-0.95||1.16|
Given this table, we can break down the contributions each team's various squads made to the margin of victory -- the Giants' passing offense was their largest positive contributor, while their rushing offense actually contributed negatively overall. In addition to the box score pages, team totals have been added to team and year pages so you can see what cumulative totals each teams' offensive and defensive squads have.
Keep an eye out for further features using this play-by-play data as the year progresses.