The first pitch is thought to be very important in an at-bat. Young pitchers are taught to get ahead in the count and that the balance of an at-bat hinges on whether this pitch is a strike or ball. Throwing first pitch strikes is a mark of a good pitcher, and one of the most infuriating things to watch is a pitcher who can't throw first pitch strikes. Today I want to look at the value of the first pitch and what happens to those pitches after they leave the pitcher's hand.

Of the twelve counts, there are six (anything without three balls or two strikes) where the at-bat is guaranteed to continue if the batter does not swing at the pitch. Assuming no swing, here are the chances of seeing a fastball in a subsequent count, based on whether the pitch is a ball or a strike. The chart is based on what will happen in the future based on what happens in the current count. So starting in an 0&0 count, if pitch is a ball, there is a 59% chance the next pitch (in the 1&0 count) will be a fastball, but if the first pitch is a strike, there is a 48% chance of a fastball being thrown in an 0&1 count. The swing of 11% measures how valuable a strike is in each count, in terms of potentially seeing fastballs.

Count   FB%     If Ball   If Strike    Difference
0&0     0.59    0.59      0.48         0.11
0&1     0.48    0.49      0.47         0.02
1&0     0.59    0.70      0.49         0.21
1&1     0.49    0.59      0.44         0.15
2&0     0.70    0.78      0.59         0.19
2&1     0.59    0.76      0.47         0.29

The first pitch of an at-bat sets the tone of the at-bat due to the conditions it creates for ensuing pitches. In terms of seeing a fastball, there is relatively little difference between an 0&1 count and a 1&0 count, but if the first pitch is a strike the pitcher has put himself in a good position as the count progresses. An 0&1 count is a clear pitcher's count and even if he throws a ball in that count, a 1&1 count is still a pitcher's count and the pitcher arrived there through pitcher's counts. However, if the first pitch is a ball, the pitcher is now at a slight disadvantage because while 1&0 is a neutral count, it has the potential to turn into an extreme hitter's count. If the pitcher does throw a strike and evens the count at 1&1, he would have presumably been under more pressure to throw a strike after the first pitch. Sal Baxamusa explores this type of pitch sequencing in more detail here and actually finds that when batters put a 1&1 pitch into play, they do better when the order was strike-ball, despite apparently having an advantage in the other sequence.

Anyway, that tangent was just to establish the importance of the first pitch of an at-bat. Now that we have a rough idea of its importance, lets look at what actually happens on the first pitch. The table below shows all first pitches, broken up by pitch type, along with certain measurements about each pitch type. Freq. is how often the pitch was thrown, S% is strike frequency, or strikes balls in play/all pitches, Called% is called strikes/total pitches, Swing% is how often the batter swung at a pitch, Sw% is how often batters swung and missed when they swung, Fo% is how often batters fouled balls off when they swung, and SLGBIP is slugging percentage on balls in ball, including home runs.

Pitch   NP      Freq.    S%     Called%  Swing%  Sw/Swing  Fo/Swings   SLGBIP
CH      6271    0.11     0.55   0.23     0.33    0.33      0.28        0.557
CB      6437    0.11     0.55   0.37     0.18    0.29      0.31        0.552
FB      35131   0.60     0.60   0.32     0.29    0.13      0.44        0.551
SL      10728   0.18     0.60   0.30     0.31    0.26      0.35        0.506
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Tot     58567   1.00     0.59   0.31     0.28    0.19      0.40        0.543

Fastballs are thrown slightly more often as first pitches than overall (60% on first pitches vs. 56% overall) which makes sense with pitchers trying to throw a strike and get ahead in the count, but generally, the rates are pretty similar for how often each pitch is thrown as a first pitch and overall. The most interesting thing to me on this chart is how often batters swing at a first pitch curveball. As a batter, a curveball isn't necessarily a pitch you would expect to see at the start of an at-bat, which probably explains the low number of swings because batters would only swing if it were a very hittable curve. This seems like a great example of how not being predictable helps a pitcher tremendously though. By occasionally throwing a curve as the first pitch, the pitcher is sometimes able to get a free strike because the batter swings so rarely.

A first pitch slider would also come as somewhat of a surprise from most pitchers, yet batters swing at that pitch relatively frequently. A slider looks more like a fastball immediately out of a pitcher's hand, so perhaps batters are fooled into swinging because of this. This would explain the low SLGBIP, because unlike curveballs where a batter is swinging preferentially at pitches he likes, with sliders, batters are swinging at a pitch they think is a fastball, but are forced to adjust their swing once the slider breaks. Overall, curveballs that are put in play lead to a SLGBIP of .484, but on the first pitch their SLGBIP jumps to .552, similar to SLGBIP for fastballs on first pitches, which supports the idea that batters are good at selecting which curves to swing at on the first pitch. One other interesting thing in the table is what happens when batters swing at certain pitches. Batters rarely swing and miss at first pitch fastballs, but they foul off those pitches so frequently that fastballs are only slightly less likely to be put in play than the other three pitch types. I'm unsure why batters foul off so many fastballs, but it might be because batters are be willing to swing at a wider range of locations and speeds if they recognize the pitch as a fastball.

In the past, I've looked at how batters of different quality are approached by pitchers. Using that method again, I wanted to see if there are differences in how these batters were pitched to on the first pitch as well. In the table below, columns labeled with -1 are the frequencies for first pitches while the columns labeled with -R are the frequencies for all other pitches.

SLG        FB-1   FB-R   SL-1   SL-R    CB-1    CB-R    CH-1    CH-R
>=.500     0.58   0.52   0.20   0.21    0.12    0.11    0.11    0.15
.499-.400  0.58   0.54   0.19   0.20    0.12    0.11    0.11    0.15
<=.399     0.68   0.58   0.16   0.19    0.08    0.10    0.08    0.13

I grouped hitters based on their Marcel projected SLG for the 2007 season and while the windows I used to group hitters are wider than in my previous examination, the overall idea is almost identical. Narrower windows would just show a more gradual increase in off-speed pitches as batters improved, but one other thing thats interesting is that it almost is as if there is a plateau for batters with a .400 SLG. A .400 SLG seems to be the level of hitter that prompts a pitcher to alter his first pitch repertoire.

Recently, I've been looking at different groups of pitchers and seeing if there are differences in the way they pitch based on their age and the quality of their fastball. I created two group, those pitchers 34 and older and those 24 and younger, and then split those two groups into pitchers with an average fastball speed of more than 91 MPH and an average speed less than 91 MPH. The table below shows just the first pitch fastball frequency for each type of pitcher throwing to each type of hitter, along with the average of all first pitches for each pitcher type.

SLG         Young/Slow  Old/Slow  Young/Fast  Old/Fast
>=.500      0.54        0.59      0.61        0.48
.499-.400   0.54        0.56      0.63        0.49
<=.399      0.66        0.62      0.69        0.63
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Avg.        0.56        0.57      0.63        0.51

The same pattern is evident here as well, with the bad hitters seeing a lot more fastballs than the other two groups of hitters. This trend holds regardless of the age of a pitcher or the quality of his fastball and the big difference between groups of pitchers is how many extra fastballs they throw to bad hitters. Even though there isn't a tremendous amount of difference between a 1&0 count and an 0&1 count, the first pitch is a crucial pitch in setting the tone of an at-bat and the importance placed on it is probably justified because of this.