I've looked at pitcher's counts vs. hitter's count before, and prompted by this comment on The Book's blog, I decided to revisit the topic. When doing research of any kind, the hardest thing to do is to find an interesting question to topic to examine, and Tango's comment had a whole lot of interesting questions, so I'm going to tackle some of those, pseudo-blog style, throughout the day. Anyway, without any more introduction, lets see some results.

The reason certain counts are considered hitter's counts or pitcher's counts is partially due to the likelihood of a fastball being thrown on that pitch. For most pitchers, a fastball is their least effective strikeout pitch, as well as the pitch they have the most control over. In an extreme example, on 3&0, most of the time a pitcher will throw a fastball to get a strike, but in doing so, gives the batter a better a good pitch to hit. The chart below shows the percentage of fastballs thrown in each count, and gives a slightly different view of what makes up a hitter's count vs. a pitcher's count.

Count    FB%    Pitches
3&0      78%       2643
3&1      76%       5083
2&0      70%       8282
-----------------------------------
3&2      61%      10096
2&1      59%      12084
0&0      59%      58849
1&0      59%      23982
-----------------------------------
1&1      49%      22900
0&1      48%      27712
0&2      47%      12943
2&2      47%      16947
1&2      44%      19802

With an average FB% of 59% and the number of pitches thrown in each count, there are four counts that see an "average" number of fastballs, while the others could be grouped into hitter's counts and pitcher's counts. Most of these percents make sense, and the top of the list corresponds very well to the top of the pass-through table in terms of ranking the counts in terms of hitter friendliness. Not surprisingly, hitters see the most fastballs in 3&0 and also have the best results if they pass through that count during their at-bat. The ranking of pitcher's counts doesn't match up as well, with 0&2 surprisingly not seeing the lowest FB%. I'm not sure exactly why this is, but the important thing is that the differences between groups is much bigger than any differences within the groups.

The "ownership" of counts changes slightly using FB% as a guide. It makes intuitive sense that 1&1 should be a neutral count, the results of plate appearances that end in a 1&1 count make it a neutral count, the pass-through results say it's a neutral count, yet pitcher's throw fewer fastballs in that count than in other ones. Pitcher's don't seem to agree that 1&1 is actually a neutral count, and have responded by throwing almost as few fastballs as they do for 0&1 and 0&2 counts. 1&0, 2&1 and 3&2 change hands too. Prior to looking at this table, I would have bet any amount of money that there were a lot of fastballs thrown in these counts, making them hitter's counts. All of them have more balls than strikes and it just seems like they favor the hitter. Tango's pass through data labels them as hitter's counts, but pitchers treat them like 0&0 counts, throwing an "average" amount of fastballs. The two gray-area counts that Tango mentions (0&1, 2&2) are both pitcher's counts by this metric.

Count   High%   Low%    Mid%
3&0     29%     27%     44%
3&1     27%     27%     46%
2&0     27%     29%     44%
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3&2     32%     26%     42%
2&1     28%     28%     44%
0&0     29%     28%     43%
1&0     27%     30%     43%
----------------------------
1&1     29%     28%     43%
0&1     31%     28%     42%
0&2     51%     18%     31%
2&2     35%     24%     41%
1&2     41%     21%     38%

Now that we know a little about what pitchers throw in different counts, let's look at where they throw it. The table above shows the vertical locations in the strike-zone for fastballs thrown in each count. In a 3&0 count, 27% of fastballs thrown are higher than 6 inches below the top of the strike-zone, 29% are lower than 6 inches above of the bottom of the strike-zone and 44% are thrown between that. This doesn't account for the horizontal position of the pitch and there really isn't anything interesting to see in most cases. 0&2 has the lowest percent of pitches in the middle, which is expected, and it seems that when a pitcher is going to throw a waste pitch on 0&2 and 1&2, it is usually thrown high.