As an act of prostest against the very sloppy Ravens vs. Jets game on Sunday night, By the Numbers has decided to ‘Suit Up‘ for a formal Week Four Review. This week we’ll discuss the game in the context of the advanced metric Win Probability Added (WPA). An explanation of WPA starts with the definition on Win Probability (WP). WP is the probability that a team wins the game given the current score, field position, down and distance. For example, at the start of the 2nd quarter, a team down by 3 points with 1st and 10 at midfield will win 46% of the time, a 0.46 WP. WPA is the difference in win probability (WP) between the start of the play and the end of the play. That difference is then credited/debited to the two teams. Because the chance of one team winning the game is directly related to the opponent’s chance of winning, the WP of the two teams always adds to 1.0. Thus, at the end of the game the winning team has a WP of 1.0 and the losing team has a WP of 0.0. The graph below shows WPA plotted as a function of time for the Ravens game against the Jets. The graph is taken from the excellent website, Advanced NFL Stats. The annotations are my own and are explained in the table below the graph. A fully interactive version of the graph is available here.
|1||Q1 – 12:18||M.Sanchez sacked at Jets 6 yard line by E. Reed. M. Sanchez fumbles, fumble recovered by J. McClain and returned for touchdown.|
|2||Q1 – 12:07||B. Cundiff kickoff from Ravens 35 yard line. Kickoff travels 7 yards deep in Jets endzone. J. McKnight returns kickoff for 107 yards for touchdown.|
|3||Q1 – 8:30||False start on M. Birk. Ravens moved back five yards to their 21 yard line.|
|4||Q1 – 8:05||J. Flacco completes short pass across the middle to R. Rice to for 52 yards.|
|5||Q2 – 14:21||M. Sanchez fumbles, fumble recovered by P. Kruger at Jets 23 yard line.|
|6||Q2 – 8:21||M.Sanchez sacked at Jets 22 yard line by H. Ngata. M. Sanchez fumbles, fumble recovered by J. Johnson and returned for touchdown.|
|7||Q2 – 6:26||J. Flacco is intercepted by D. Harris. D. Harris returns interception for touchdown.|
|8||Q3 – 9:13||J. Flacco sacked at Ravens 22 yard line for by A. Maybin. J. Flacco fumbles, fumble recovered by M.Dixon.|
|9||Q3 – 9:03||M. Sanchez intercepted by L.Webb. L. Webb returns interception for touchdown.|
|10||Q4 – 9:51||R. Williams carries to the right, tackled by C. Pace. R. Williams fumbles, fumble recovered by S.Pouha.|
WPA is a narrative statistic not a predictive statistic. In other words, WPA does an excellent job of telling us what the “big plays” were in a game but it doesn’t tell us anything about what to expect in the future. Its a great statistic for reviewing but a poor one for previewing. The graph above shows how sensitive WPA is to context. For example, Joe Flacco’s fumble (8) that occurred midway through the 3rd Quarter with Ravens leading by 10, cost .10 WP taking them from an 83% chance of winning to a 73% chance. However, Ricky Williams fumble (10) midway through the 4th Quarter with the Ravens leading 17 barely registered a blip on the WPA graph.
Overall, the graph shows us how valuable the Ravens defense was on Sunday. Pagano’s boys recorded two different plays (1 and 9) that added at least .20 WP, setting the tone for the game early and securing it late. .20 WPA plays are rare due to context and skill so its no surprise that in the same game the Ravens Defense scored a franchise record 3 TDs they recorded two plays of at .20 WPA.. The result is a team that has excellent prospects heading into the bye week at 3-1. Tomorrow we’ll look forward and project this team for the rest of the year using several models from Football Outsiders.