In addition to the daily analysis and normal statistical offerings, FanGraphs has some other pretty useful and powerful features. Anchoring a lot of those features are the Depth Charts, which in addition to providing information on their own, power the playoff odds and projected standings we host on the site.
The Depth Charts are pretty simple in theory. They blend together two of the leading projection systems (Steamer and ZiPS) and then scale those projections to our expectations about playing time. The Depth Charts are updated constantly to provide the most up-to-date snapshot possible for the current state of a team, league, or position. You can think of the Depth Charts as the baseline projections for the entire site, as they are the input for the projected standings, playoff odds, and game odds.
How The Depth Charts Work:
Every team has a page on our Depth Charts divided up by position. By rule, we assume a team will get 640 PA from catchers, 700 PA from the other offensive positions, and about 1,500 innings of pitching in some form. Our writers take the rosters of each time and divide up the playing time based on our beliefs about how those players will be used.
If a player gets hurt, we dock their expected playing time. If a player takes the reins when given a chance to start, we bump up their playing time. Our staff constantly monitors news from around the league and updates these expectations in real time. Sometimes a change won’t show up for a few hours, but you will commonly see it reflected within thirty minutes. If you ever see a playing time estimate that looks odd, or if a player has somehow ended up on the wrong team, give one of our writers a shout so we can correct it. August Fagerstrom is our Depth Charts Czar if you want to go straight to the top.
Once we know who is going to play where, then we draw in projections for each player based on Steamer and ZiPS projections. We give equal weight to both systems, so if a player has a .400 projected OBP from Steamer and a .380 projected OBP from ZiPS, we give that player a .390 projected OBP. We call this the “Depth Chart Projection.”
Keep in mind that we get access to the full Steamer projections earlier in the offseason than the full ZiPS projections, so we rely exclusively on Steamer from November to about March. During the season, both systems are used. We make no individual changes to the projections and the only FanGraphs influence in the output comes from our playing time estimates.
What The Depth Charts Show:
As far as the basic Depth Charts are concerned, there are essentially three different views. You can look at a team’s Depth Chart, you can look at the league Depth Charts by position, and you can look at the summary data of both of those at one.
Keep in mind that the Depth Charts are showing what we expect to happen for the rest of the season, not the stat line we expect them to end the season with. If a player has a .400 OBP through 40 games, we are showing what we expect their OBP to be from Game 41 to Game 162. The Depth Charts are about future performance.
As far as viewing options, you can look at the Depth Charts in team view, in position view, or in summary view. In team view, you get a breakdown of a single team by position, meaning on the Blue Jays page there’s a box for catchers, first basemen, etc. Each team also has a box for all positional players and all pitchers, as well as a box on the right that shows you where they stand overall compared to the rest of the league.
In position view, you can look every team’s Depth Chart at any one position. For example, here is the page for catchers. This allows you to compare positions around the league and see which group of backstops is most valuable. Obviously these rankings are based on the projection systems and our playing time estimates, so if you believe playing time will shake out differently that we do, you might expect to see a different overall ranking.
Finally, this handy grid collapses those two views into one. You can’t see all of the players in that view, but it puts together each team’s expected WAR at each position so that you can quickly compare how teams and positions stack up against each other.
Using The Depth Charts:
The Depth Charts are very useful for a couple of reasons. First, they blend two projection systems together without you having to do any of the work, and that’s helpful because aggregate projections are better than any one system. As an added bonus, under the Projections tab at the top of any site page, you can find a link that takes you to the Depth Charts projections as a normal table of statistics without the team and positional dividers.
Second, playing time is controlled by humans. While projection systems are much better than people at forecasting performance, projection systems aren’t very good at figuring out how much playing time a player is actually going to get. Finally, the Depth Charts gather a lot of information in one place. We’ve had projections on the site for years, but having them built into the system like this allows you to make a lot of comparisons and see where teams are strong or weak.
Keep in mind that the Depth Charts are only as good as the inputs. If you don’t like Steamer, ZiPS, or our estimates of playing time, you might not find them useful.
These Depth Charts are the backbone of some of our other features, as well. Our rest-of-season projections and playoff odds are built using the Depth Charts to determine the quality of the teams involved the rest of the season’s games.
Neil Weinberg is the Site Educator at FanGraphs and can be found writing enthusiastically about the Detroit Tigers at New English D. Follow and interact with him on Twitter @NeilWeinberg44.