Strikeout Quality: Actual vs. Expected Strikeout Ratio – 2010

Traditional measures of a pitcher’s strikeout ability focus on the actual number of strikeouts or the number of strikeouts per nine innings. One of the misleading parts of these measures, though, is that they do not reflect the strikeout frequency of the batters faced. If a pitcher faces batters that strikeout often, that pitcher would be expected to have a higher number of strikeouts and a higher rate of strikeouts per 9 innings. What would be helpful in determining the quality of a strikeout is an adjusted strikeout measure that reflects the strikeout frequency of the batter faced.

To do this, you would need to look at the pitchers actual strikeouts in relation to the number of strikeouts the pitcher would be expected to have given the batters they face. For each batter, I calculated the strikeout frequency for the season, and took this as the frequency with which the average pitcher would strikeout this batter. I then compared the number of times a pitcher actually struck out the batter to the number of times it is expected that an average pitcher would strike out this batter. If the number of actual strikeouts is higher than the number of expected strikeouts, then the pitcher is striking out batters at a higher rate than average. If it is lower, the pitcher is striking out fewer batters than average. I have labeled this ratio the AESR (Average vs. Expected Strikeout Ratio), and it is simply calculated as the actual number of strikeouts divided by the expected number of strikeouts.

2009 Results

The top 10 pitchers in terms of AESR from 2009 were:

Of the pitchers with the top 10 AESR’s in 2009, only three of them made the top 10 in 2010.

2010

For 2010, the pitchers with the top 10 AESR’s (at least 100 innings pitched) are:

Of the pitchers that were in the top 10 in 2009, the pitchers that stayed in the top 10 in 2010 are Jon Lester, Justin Verlander, and Tim Lincecum. Lester remained at 4, while Verlander dropped from 1 to 7 and Lincecum dropped from 3 to 10.

There are also some interesting insights when comparing the AESR rank to the strikeouts per 9 innings rank. Brandon Morrow had the highest AESR and the highest number of strikeouts per nine innings, and was significantly better than the second ranked pitchers in both categories. However, there were significant differences between the AESR and strikeouts per nine innings rank for many of the other pitchers. Of the pitchers in the top 10, Lincecum had the largest negative difference between the AESR rank and the strikeouts per nine innings rank. He was ranked second in strikeouts per nine innings but 10th in AESR. This was due to the fact that although he had 231 strikeouts, the batters he faced struck out more often than average, so his AESR suffered as a result. Conversely, American League Cy Young winner Felix Hernandez had an AESR rank that was 17 places higher than his strikeouts per nine innings rank. His rank in strikeouts per innings pitched was significantly lower because he pitched significantly more innings. He pitched more than 25 innings more than any other pitcher in the top 10, and was second in the major leagues only to National League Cy Young winner Roy Halladay who pitched 250 and 2/3 innings.

Career

The top 10 pitcher AESR’s for pitchers that have pitched more than 2000 innings since 1974 is shown below.

On this list, there are no pitchers that were active in 2010. Interestingly, as dominant a performance as Morrow had in 2010, there are three pitchers who, for their career, have a higher AESR. Nolan Ryan sits significantly above the rest of the field.

Of the pitchers that were active in 2010, the top 10 AESR’s are shown for pitchers with at least 1,000 innings pitched.

Of the pitchers on this list, five are starters and barring any unforeseen circumstances would get to 2,000 innings pitched. Santana is the closest to 2,000 innings pitched, and he would rank 6th on the all time list. At their current AESR, Beckett and Kazmir would make the top 10 in 10th place. It looks as if the top 5 spots are solidified for at least the near future.

Over the next few weeks, in preparation for the start of the 2011 season, I will look at the strikeout performance of the top 5 pitchers in more detail.