F/X VisualizationsAugust 07, 2009
Regression and Pineiro
By Dave Allen

Recently there has been some discussion about estimating a player’s true talent level. The idea is that a player's true talent, and how we should expect him to perform going forward, is not the player’s current level of production. Rather it is a weighted average of his current year and past production (with more recent production weighted more heavily) and then this average is regressed to league average, with the amount of regression depending on how many plate appearances (for batters) or batters faced (for pitchers) or inning played (for fielders). The details of how to do the weighting and to which population’s mean you regress are important and discussed at the Book Blog and THT.

I wanted to look at an example of a player whose current year production is far out of line from a long career of established production. Joel Pineiro leads all starters in ground ball rate, at 60.4% ground balls per ball in play. Since 2002 his GB rate ranged between 44% and 48%. In addition, Pineiro leads all starters league in BB per batter faced at 2.6%, again far out of his previous range of 5.4% to 8.5%. This is a rather huge shift in his numbers.

Here are his five pitches.


The movement on these pitches is fairly standard. It is important to note his two-seam fastball ‘sinks’ compared to his four-seam fastball. Here is the breakdown of his pitch usage over the past three years, those covered by PITCHf/x.

|                    | 2007 | 2008 | 2009 |
| Four-Seam Fastball | 0.54 | 0.36 | 0.11 |
| Two-Seam Fastball  | 0.03 | 0.23 | 0.60 |
| Slider             | 0.16 | 0.20 | 0.11 |     
| Curve              | 0.16 | 0.09 | 0.09 |     
| Changeup           | 0.11 | 0.12 | 0.09 |     

His two-seam fastball is hit on ground just under 68% of the time it is put in play, so his increased usage of that explains the jump in grounders. He gets his fastballs in the zone about 54% of the time while his breaking and off speed pitches are in the zone under 50% of the time (47% for his change, 42% for his curve and 49% for his slider). Finally batters swing at and make more contact with his fastballs than his off-speed and breaking pitches. As a result he has many fewer walks and strikeouts (he has struck out just 10% of batters the lowest rate in his career).

I think this is an interesting example in which the PITCHf/x data partially explains a recent abrupt change in numbers. Obviously we do not expect Pineiro to continue to walk under 3% of batters faced and get over 60% of his balls in play on the ground. An estimate of true talent and expectation going forward must include some weighting of past performance and regression to the mean. But I think the PITCHf/x data, just like scouting data, can be used to adjust the weighting, maybe weight this year even more heavily if we expect him to use this pitch break down going forward, or regress to different pool, one with this breakdown of pitches, to get a better estimate of his true talent going forward.


Excellent review of why Pineiro is performing differently this year than in the past and how PITCHf/x data can be used to project future performance. Thank you as always.

It's interesting. When you combine looking at data like this to what Brian Bannister has done - namely, dramatically increasing his GB rate, perhaps there is something to the blind spot of FIP in that GB rate is more controllable to a pitcher than his HR rate, and that it can have a drastic effect on performance. Perhaps there is something to the old Atlanta Braves school of thought of throwing sinking fastballs and sliders low and away from hitters and getting them to drive that ball into the ground consistently.

Yes, JayM, we would agree with you. There is a certain level of randomness when it comes to home runs, perhaps best reflected in the HR/FB rate. Substituting GB % for HR rate smoothes that out a bit. To the credit of Dave Studemund at THT, he developed Expected Fielding Independent Pitching (or xFIP), which adjusts FIP by normalizing the HR component.

By the same token, we've been categorizing pitchers by K and GB rates for years and began to rank them using K, BB, and GB % z-scores earlier this year.

What we have found is that strikeouts have the greatest impact on ERA and RA, followed by walks, and groundballs. With the plus sign indicating above average and a minus sign below average, the order of importance of these three defense independent pitching stats is as follows: K+ BB+ GB+ > K+ BB+ GB- > K+ BB- GB+ > K+ BB- GB- > K- BB+ GB+ > K- BB+ GB- > K- BB- GB+ > K- BB- GB-.


As Rich points out that the HR/FB rate is an important limitation of FIP and xFIP is a great alternative. Another is tRA, developed by Graham MacAree, it gives pitchers credit for Ks and BBs just like FIP. Beyond that it gives pitchers credit for each batted ball type. So if a pitcher gets lots of pop ups his tRA will be lower, and if he gives up lots of line drives or flyballs his tRA will be higher. The stat is available at Graham's and Matthew Carruth's website and is explained here.

Rich I had forgotten about that study. It is really interesting that K+BB-GB- pitchers come out better than K-BB+GB+. It really shows the power of the strikeout. Pineiro is interesting because he about as extreme K-BB+GB+ as you can get. Once his HR/FB regresses he doesn't look quite as good, and I don't think he can keep his walks that low going forward. But it is cool to see how he can succeed with almost no strikeouts.

Pineiro is about as extreme as a pitcher could be and, therefore, makes a great case study. He has been as good as a pitcher with that low of a strikeout rate could almost ever hope. Joel pitched today, allowed only his fourth HR in 2009, struck out six (tied for the second most this year), and did not walk a single batter for the 12th time in 22 starts while completing seven innings and recording the win as STL beat PIT 7-3.

I will be interested to see how he performs the rest of this season and over the course of the remainder of his career.

P.S. - I have added Stat Corner to the links in our sidebar.