Saturday, December 04, 2010

Pitching Percentiles

Many fans like the traditional statistic Earned Run Average (ERA) because they are so familiar with its values.  They know that an ERA under 3.00 is very goodf for a starting pitcher and than an ERA over 5.00 is poor.  One difficulty many fans have when they are introduced to a new measure is that they don't know what values of that measure are good and bad.  When they hear about pitcher ground ball percentage (GB%) for the first time, it might sound like a good concept.  However, if they hear that their favorite pitcher has a GB% of 50%, they might not know how that compares to other pitchers.

One of the most popular features of my book Beyond Batting Average is a series of simple percentile charts which help give fans an idea as to which values of a statistic are good and bad by comparing them to a familiar statistic like ERA.   The table below shows the percentiles for  some of the less traditional pitching statistics and puts them next to the equivalent percentiles for ERA.  This makes it easier for fans to grasp some of the newer statistics.  The chart includes all MLB starting pitchers with 15 or more games started in 2010.

One can see from the table that the 75th percentile for ERA was 3.50.  This means that 75 percent of starting pitchers had an ERA under 3.50 and 25% over 3.50.  A pitcher with 7.8 strikeouts per nine innings (k9) would also be at the 75th percentile.  So, we can say that a k9 of 7.8 is as good as an ERA of 3.50.  Similarly, a k9 of 4.8 would be bad because it's equivalent to a 5.40 ERA (10th percentile).

The statistics in the chart can be found on FanGraphs.com. They are defined as follows:

ERA = Earned Run Average
WHIP = Walks Plus Hits Per Innings Pitched
K9= Strikeouts per nine innings
BB9 = Bases on Balls per nine innings
K/BB = Strikeout to Walk Ratio
GB%= Ground Ball Percentage
BABIP= Batting Average on Balls in Play


A similar table showing how batting statistics compare to batting average was included in an earlier post. 


Table 1: Pitching Percentiles for Starters, 2010

2 comments:

  1. Andrew in TorontoDecember 06, 2010

    Typo: "One can see from the table that the 75th percentile for batting average was 3.50." Should be earned run average.

    Do you weight the data by innings pitched / plate appearances? It might be a good idea, to avoid the percentiles being skewed by a long tail of spot starters.

    ReplyDelete
  2. Andrew,

    Thanks for pointing out the typo.

    I have not weighted by IP or PA. I try to keep things simple when presenting a teaching topic like this. I might explore some kind of weighting to see how it looks though. I think it should not affect the comparisons. If ERA is skewed, then other pitching statistics should be skewed along with it.

    ReplyDelete

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