# Win Values Explained: Part Two

This afternoon, we looked at the offensive side of the Win Value equation. Linear weights are pretty widely accepted now, and since wOBA and wRAA match up so well with what people understand about offensive value (Albert Pujols had a good year, Jeff Francoeur did not), it’s not a big surprise that there isn’t much questioning that part of the formula. We get into a bit stickier water when we move to the Fielding side of things, however.

In the Win Values calculations here, Fielding is fairly straight forward – it’s simply a player’s total UZR at all positions for the given year. We talked a lot about UZR the last few weeks after it was added to the site, but if you’re looking for a more detailed explanation of the system, the introduction can be found in part one and part two. Essentially, it’s the best fielding metric publicly available, and while it’s not perfect (I generally give it an error range of five runs in either direction, meaning that a +10 could be anything between a +5 and +15), it’s a big step forward in defensive evaluations.

UZR, unlike the offensive component wRAA, is relative to the league average of the position for that player. We talked about this a few weeks ago in talking about how to read the UZR numbers. +15 in LF is simply not an equal performance to +15 in CF, as the players they are getting compared to are drastically different. This creates the need for position adjustments to account for the difference in quality between positions. However, when displaying the Win Values here, we’ve broken them out into separate components to be as transparent as possible, so the Fielding numbers do not include the position adjustment. We’ll get to those next. The fielding total is simply a sum of the players UZR from each position he played in the given year.

The current version of UZR on FanGraphs does not include a few minor things, such as the value of arm strength and turning double plays. Some of these will be added in soon as MGL updates the data, but the changes are going to be minor – despite the emphasis put on it by many, there just isn’t a huge difference betwee most major league players in terms of the runs saved through their throws from the outfield. However, if you feel like a particular player has an exceptional arm and should be rewarded for it, feel free to add in a couple of runs to make up for the fact that UZR doesn’t include that portion of his defensive value.

The other important point to make here is that you’ll notice that catchers have no values entered in the Fielding portion of their Win Values. Evaluating catcher defense is something we’re simply not very good at right now, and while there are strides being made (including a great article by Tom Tango in the 2009 Hardball Times Annual), there’s a lot of things that we haven’t figured out how to quantify yet. So, we’ve just left catchers alone, ranking them all as league average, and will let you all adjust their final win value however you’d like to reflect their defensive value relative to other catchers.

If you think Joe Mauer‘s catching abilities and leadership are worth one win, just add one win to what we display as his win value here. Quantifying catching defense is something that we just haven’t figured out yet, and so we’re not pretending that we have. Consider it an opportunity to fill in the blanks.

Tomorrow, we’ll look at the position adjustments and how the wRAA, UZR, and position adjustments add up.

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Dave is the Managing Editor of FanGraphs.