Win Probability is a fun statistic. It's also a fluctuating one. When Haloti Ngata and Terrell Suggs stuffed Mark Ingram on 4th-and-goal from the 1, the Ravens WP improved by nearly 10%. Later, Juice fumbled a ball that almost certainly cost the Ravens a touchdown. That lowered their WP by 17%. Later, when Drew Brees dropped back to pass on third down midway through the third quarter, the Ravens had a 48% chance of winning the game. Will Hill stepped in front of the poorly thrown ball to return it to the house for six points, which caused the Ravens chances to shoot up to 79%.
Win Probability is at its core a team and game statistic that incorporates historical data for games with similar scores, down/distance, time remaining etc. to apply a probability that a particular team will win.
However, although the NFL is the world's quintessential team sport where individual contribution can be difficult to separate from one's teammates, Win Probability can help close the gap on quantifying an individual player's impact on winning.
When Will Hill produced the pick six, he himself received the 31% boost in Win Probability Added. In essence, WPA is an attempt to quantify a player's direct contribution to a team's victory in a particular game. When we aggregate it over the season, we start to get an idea of who is doing the most to help their team win. Hardly perfect, it is a useful metric nonetheless and does better than many others.
Haloti Ngata and CJ Mosley dominant
Haloti Ngata had a brief run in 2010 and 2011 where not only was he probably the Ravens best defender (he was by PFR's Average Value), but he had the reputation of the best defensive tackle in football. While new blood like J.J. Watt have overshadowed some of the elder players, Ngata has quietly had one of his best seasons of his career. After yesterday's victory, Haloti Ngata now leads all defensive tackles in Win Probability Added. It's not especially close either. Ngata is just flat out dominating. His closest competitor, Gerald McCoy, just signed a $100 million deal this year.
Not to be outdone, C.J. Mosley continues his amazing rookie year. He remains second in the NFL among all linebackers. Let me just be the first right now to laugh in the face of anyone who would argue that C.J. Mosley is anything but a serious contender (if not frontrunner) for DROY or that his success is merely the product of the Ravens' front 7. False.
WPA is really valuable here because it cuts through the subjective arguments like "eye-test" and other qualitative reasonings (like draft status, which always influences popular perception). To get a quality WPA, you have to be the one making the plays, period. Your teammates can help out to a degree by doing their jobs (it will always be a team sport) but they can't make the play for you. You only get WPA by having a direct part in a play that elevates your team's chances to win.
It is actually quite easy to illustrate WPA's validity. Consider the Houston Texans. Not an especially good football team though far from the worst. However, J.J. Watt is almost universally considered the leader for DPOY and were this a fairer world, MVP, too. If you've watched anything Houston did this year, you would see immediately that Watt has been a terror. Your eyes would not deceive you.
WPA confirms just how vast the chasm is between Watt and everyone else at the Defensive End position. It ain't even close. WPA takes what we thought might be true (that Watt is dominating as part of a fairly average team) and shows us that the gap between he and the second best DE by WPA is bigger than the second best guy and the 45th one. It's the sort of dominance that would be easy to miss if you didn't watch the Texans' games and focused instead on someone like Arizona who is one of the best NFL defenses and records to boot.
This is a reason why WPA is valuable. We have lots of good stats out there for teams like DVOA and so forth. But in a game that relies on 11 facing off 11 other players, it can be a struggle to really measure an individual player's contribution, particularly on defense which lacks for the reliable counting metrics that offense has. WPA is one way and a pretty good one at that.
Mosley's and Ngata's high-caliber play may be apparent to us watching them each week but rest assured your eyes do not deceive you. They are every bit as good this year as you think.