As you know by now, FanGraphs is hosting a new projection system year, the Fan Projections. Dave Cameron filled us in on why projecting players in this manner can be effective, thanks to the wisdom-of-the-crowds idea. My piece of wisdom to impart is the value of pitch data to inform your projection. This data can tell you if a pitcher has gained or lost speed on his fastball, picked up a new pitch or is throwing a certain pitch more or less often. Thus it is another tool in diagnosing if a big shift in pitcher performance was luck-based or a shift in true talent. You can find that data in the pitchf/x section of each pitcher page or in the Pitch Type section (these pitch classifications are from BIS, which can be slightly different than the pitchf/x ones).
A fitting example is Brian Bannister, a pitchf/x devotee himself. Although we don’t ask you to project it here, one value you could project is his 2010 GB%, which will heavily influence his HR/9 and ERA. Here are Bannister’s GB%s over his career (in green).
Using a Marcel-like 5/4/3 weighting of the past three years to project his 2010 GB% we would get around 43% . But we know that Bannister is a much different pitcher in 2009 than he was in 2008 and 2007. In 2007 and 2008 he threw almost 60% fastballs, but in 2009 he threw the fastball just 17% of the time and a previously unused cutter 50% of the time. This change in pitch type supports the change in GB%, since cutters tend to result in more ground balls than fastballs, and makes us more confident this increase in ground balls is for real going forwards.
We still want to regress somewhat to prior performance and league average, but the change in pitch usage means we should value 2009 more heavily, and project him around 47% or so. From there we can project his HR/9 and ERA based on the assumption that he is above average at getting grounders.