Why is Offense Down?

Three weeks into the major league season, scoring dropped half a run per game through the same point in the previous season.  What caused this drop?  It could be the umpires, but looking at heat maps of called balls and strikes, there is no discernable difference in the frequency of strikes called outside the strike zone and balls called inside the strike zone.  The same errors exist in the same locations.

Batter selectivity then came into question.  Again, looking at heat maps, the only bit that looked different was that maybe batters were taking more strikes down the middle of the plate, and maybe they were taking more high strikes.  These were minor differences at best, probably accountable due to the sample size early in the season.

Combing through the data, the one thing that stood out was a change in the frequency of certain pitches:

Through the first 22 days of the season.

Pitch Type	2010	2011
Fastball	51.4%	46.4%
Change	12.5%	12.3%
Curve	9.5%	9.5%
Slider	14.6%	14.9%
Cutter	4.7%	5.5%
Sinker	6.3%	9.7%

Fastballs are down, and pitchers are replacing them with cutters and sinkers.  Batters are chasing those pitches out of the strike zone.

Batter swings at cutters and sinkers outside the strike zone, 2010 on the left, 2011 on the right.This season, when batters swing at pitches outside the zone they produce a .191 wOBA. When they swing at pitches inside the strike zone, their wOBA jumps to .323.  Pitchers as a whole changed the way they approached batters, and that caused them to swing more at pitches with a low probability of success.

The changes hold up across the two leagues as well, although the AL is substituting more sinkers and the NL more cutters. 

Batters are seeing a different mix of pitches than usual, and they'll need to adjust if offense is to recover.

Mariano Rivera's Pitch Frequency

With the first game of the ALCS less than an hour away, let's take a quick look at the pitch frequency for a player that has been so instrumental in the New York Yankees postseason success: Mariano Rivera.

As the heatmap below shows, Mariano Rivera has an amazing ability to command the strike zone.

Mariano Rivera's 2010 Pitch Frequency vs. All Major League RHP Notice how Rivera barely touches the middle of the plate.

Here are Rivera's Righty-Lefty heatmaps vs. the rest of the league:

Mariano Rivera's 2010 Pitch Frequency against LHB (439 pitches) vs. All 2010 Major League PitchersMariano Rivera's 2010 Pitch Frequency against RHB (476 pitches) vs. All 2010 Major League PitchersAs you can see from the top map, Rivera lives on the inside corner to lefty batters.  In fact, the majority of his pitches fall outside the designated strikezone.  Meanwhile, the rest of the league favors throwing down and away to LHB.

Against RHB, Mo spreads out his pitches a bit more.  However, notice how he barely ever throws to the middle inside part of the plate to righties.  He also busts righties up and in, again in contrast to the rest of the league.

As a matter of comparison, here are the pitch frequency heatmaps for 3 other AL closers:

Rafael Soriano's 2010 Pitch Frequency (890 pitches) vs. All 2010 Major League RHPJoakim Soria's 2010 Pitch Frequency (1086 pitches) vs. All 2010 Major League RHPNeftali Feliz's 2010 Pitch Frequency (1072 pitches) vs. All 2010 Major League RHPAll three of the above closers tend to pitch to the middle of the plate, a striking contrast to Rivera's pitch frequency.

Lastly, here's a look at Rivera's pitch frequency since 2008:

Mariano Rivera's Pitch Frequency since 2008