Lately, I've been trying to come up with a defensive equivalent to the goals created statistic. Ideally, I would like to be able to add the two, and come up with an overall value of each player. I'm not quite there yet, but I've found something that makes sense for defensive contribution. When looking at Marginal Goals, we can determine how many goals (compared to a fictional "marginal" team) we prevented. With the percentage of shots saved by the goalkeepers, we can break it down further to see how many goals were prevented by the keeper, and how many were prevented by outfield players.

In the 06/07 season, I rated our outfield defence 15.768 goals better than the marginal team (think Sunderland of 05/06). How do we divide this up among individuals? The most fair method I've come up with this equation:


Here, we have MGP for marginal goals prevented; DA as defensive actions - including all clearances, blocks, interceptions, tackles, and offside provocations; and M as minuses - the number of goals conceded with a player on the pitch. The same variables with a lower-case t are the team totals for each. This gives us the following table for 06/07:

So what this means is that, by having Aaron Hughes start at CB instead of a generic player from the 05/06 Sunderland team, we prevented almost 3 goals. Brede Hangeland and Dejan Stefanovic still managed to prevent almost 2 goals apiece in their limited time. I think that all of this tells us that there isn't a huge difference between our top 4 CBs, but the difference does amount to about half a win, or 1-2 draws. As we have found out, that can be the difference between staying up and being relegated.

Another thing I found interesting is how this relates to our current central midfield dillema. I predicted that Danny Murphy and Jimmy Bullard will finish this season with almost exactly the same total of goals created, with roughly the same number of minutes. In defence, however, they differ quite a bit. Murphy, while not an idea defensive midfielder, was still ahead of Bullard. Leon Andreasen, projected over a full 3000-minute season, would have been more than a full goal better than Bullard. Would that goal make up for the loss in attacking ability? Or would Andreasen's presence allow Murphy and the rest of the team to attack more effectively? It's all difficult to say, but we're getting a little bit closer to understanding just what it means to replace a player in the lineup. The fun begins when we can look at marginal goals created. That's (hopefully) coming soon, and it should give attack and defence statistics a common ground, a way to say "Player A is better than Player B".