Tiger Tales: A Detroit Tigers Blog

Today, I’ll continue with the batted balls versus pitchers theme which I started earlier this week. An at bat can result in any of the following events:

• Strikeout
• Base on balls
• Hits batsman
• Ground ball
• Line drive
• Outfield fly
• Infield fly

Three of those events are generally favorable events for pitchers:

• Strikeout
• Ground ball
• Infield fly

I will call these run preventing events (RPE). Of course, a ground ball is not as easy an out as a strikeout or an infield fly and can have a negative result for a pitcher. However, inducing a lot of ground balls will help to prevent runs over the course of a season. On the other hand, it is good for pitchers to avoid, for the most part, the following events:

• Base on balls
• Hits batsman
• Line drive
• Outfield fly

So, I thought it would be interesting to calculate the run preventing event percentage (RPE%) for American League pitchers in 2006 where RPE% = (SO + GB + IFF)/BFP. Striking out batters and inducing grounders have been shown to be repeatable skills. Getting batters to hit infield flies is not stable from year to year (correlation = .10 between 2005 and 2006). However, infield flies are relatively rare compared to other batted ball types and including them does not change the RPE% substantially in most cases. Plus, I suspect (without statistical evidence) that this is a real ability for some power pitchers.

It turns out that RPE% is fairly stable with a .66 correlation between 2005 and 2006. It can also be considered a fielding independent stat because, although the end result is not independent of fielders, getting a grounder or infield fly to happen in the first place has nothing to do with fielders. It is as stable or more stable than FIP ERA but it is not weighted and thus does not explain as much about runs allowed. RPE% is just an exploratory stat for now.

There were 48 American League starters with 125 or more innings pitched in 2006. Table 1 lists the RPE% rankings for Tigers starters. Table 2 lists the top 20 pitchers in the league. We can see that Jeremy Bonderman (RPE%=.585) ranks very well (6^th in the AL) as he does on most fielding independent stats. Kenny Rogers (ranking 14^th with .538) and Nate Robertson (16^th with .536) are also in the top third in the league. Justin Verlander (27^th with ,506) is in the middle of the pack and will likely need to improve his strike out and/or ground ball rate in 2007 if he is going to keep his ERA down.

Table 1: Run Preventing Events for Tigers Starters in 2006

Table 2: Top 20 AL Starters by RPE% in 2006