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Squaring it up

Patience is bitter, but its fruit is sweet.
- Jean-Jacques Rousseau

Usually, when we think about plate discipline, we focus on the ability to draw walks. We look at things like walk rate or strikeout-to-walk ratio and we remind ourselves how walks are very valuable, that batting average, which ignores walks, is a flawed statistic, etc, etc, etc.

But another aspect of plate discipline isn't talked about so much—not only do you walk more often when you "lay off the bad ones," but balls in play turn out much better if they were initially headed toward the strike zone.

That makes intuitive sense, but can we quantify how much better it is to swing at strikes than balls? This is not as easy at it sounds, because generally if a batter swings at a pitch, we don't know if it would have been a strike or a ball. However, we now have precise pitch location available from the pitch-f/x data, and we do know if a pitch would have been a ball or strike and so we can begin to see how much advantage there is in swinging at pitches within the strike zone.

Speaking of the strike zone, as I showed in a previous article (The Eye of the Umpire), the actual strike zone called by major league umpires differs significantly from the strike zone as defined in the rulebook. For this study, I'm going to use the real strike zone, as I measured it, and not the fictitious rulebook zone. This is crucial: The actual strike zone is the one implicitly understood by umpires, batters and pitchers. It's the relevant strike zone for an analysis like this one.

And one quick caveat, before we start digging into the good stuff: As I wrote in the above article, some fraction of pitches, perhaps 5-10%, are mistracked by the pitch-f/x system and the location data for these are not dependable. Since we do not yet have a way to know which pitches are affected, they are necessarily included in our data sample. This means there is some small degree of uncertainty in the numbers I'm going to present below, but the general conclusions will still hold. OK, let's get going.

Making contact

The first thing I looked at was swing-throughs: how often a batter swings and misses when the ball is in the strike zone or not. The following table, which is based on roughly 43,000 pitches that batters swung at, shows how often a pitch was missed, hit into foul territory or put in play:

Swing outcomes
+--------------+--------+--------+-------+--------+
| inStrikeZone | swings | missed | foul  | inPlay |
+--------------+--------+--------+-------+--------+
| No           |  14053 |  0.327 | 0.356 |  0.317 |
| Yes          |  28744 |  0.127 | 0.389 |  0.484 |
+--------------+--------+--------+-------+--------+

That's the general trend, but it's more fun to look at specific batters, isn't it? First let's look at the batters who swung most often at pitches out-of-zone:

Batters who swing at many bad pitches
+------------------+--------+-----------+--------------+------------+
| batter           | swings | ball_frac | missedStrike | missedBall |
+------------------+--------+-----------+--------------+------------+
| Anderson_Garret  |    158 |     0.544 |        0.056 |      0.314 |
| Crawford_Carl    |    133 |     0.489 |        0.191 |      0.308 |
| Diaz_Matt        |    180 |     0.478 |        0.128 |      0.279 |
| Phillips_Brandon |    104 |     0.471 |        0.127 |      0.306 |
| Thorman_Scott    |    214 |     0.463 |        0.157 |      0.364 |
| Erstad_Darin     |    148 |     0.459 |        0.063 |      0.206 |
| Kemp_Matt        |    113 |     0.451 |        0.242 |      0.451 |
| Francoeur_Jeff   |    325 |     0.443 |        0.193 |      0.264 |
| Suzuki_Ichiro    |    381 |     0.428 |        0.046 |      0.153 |
| Soriano_Alfonso  |    166 |     0.428 |        0.189 |      0.282 |
+------------------+--------+-----------+--------------+------------+
Legend:
ball_frac = fraction of swings at pitches outside the strike zone
missedStrike = fraction of misses on balls in strike zone
missedBalls = same for balls outside the strike zone

And now let's look at the guys who tend to get a good pitch to hit:

Batters who swing at few bad pitches
+-----------------+--------+-----------+--------------+------------+
| batter          | swings | ball_frac | missedStrike | missedBall |
+-----------------+--------+-----------+--------------+------------+
| DeRosa_Mark     |    109 |     0.174 |        0.133 |      0.316 |
| Vazquez_Ramon   |    125 |     0.200 |        0.090 |      0.560 |
| Glaus_Troy      |    227 |     0.203 |        0.182 |      0.370 |
| Iguchi_Tadahito |    310 |     0.210 |        0.118 |      0.308 |
| Giles_Brian     |    190 |     0.211 |        0.053 |      0.250 |
| Lofton_Kenny    |    282 |     0.216 |        0.059 |      0.213 |
| Cust_Jack       |    202 |     0.223 |        0.318 |      0.600 |
| Cameron_Mike    |    336 |     0.229 |        0.143 |      0.584 |
| Quinlan_Robb    |    113 |     0.230 |        0.138 |      0.308 |
| Johnson_Dan     |    180 |     0.233 |        0.087 |      0.357 |
+-----------------+--------+-----------+--------------+------------+

These names were more surprising to me. I was expecting to see some of the walks leaders here: Swisher, Hafner, Ortiz, those guys (see below for word on Barry Bonds). There is a wide range of bat control represented here, from good (Lofton, Giles) to average (DeRosa, Iguchi) to terrible (Cust). Cameron and Vazquez are OK on balls in the strike zone, but whiff mightily on balls outside the zone, although small sample size is an issue for some of these batters.

This is a good time to remind you that the pitch-f/x data is not complete: Many players are excluded from this analysis because the system is not installed in their home parks. For example, I have only 39 Barry Bonds swings in my database, so he doesn't make any of these lists. So, these lists should really be considered not the best, but some of the best.

Squaring up the strikes

But what about when the batter manages to put the ball in play? Once he does that, does it matter whether the ball was inside or outside the strike zone? How many times have we seen a guy like Vlad Guerrero drive a ball that is six inches off the plate into an outfield gap, or indeed over the fence? Should Vlad lay off those pitches?

Well, yes, he should. Here's what happened on balls put into play for pitches that were in the strike zone and pitches that were not:

Outcome of balls put in play
+--------------+--------+------+------+------+------+------+------+
| inStrikeZone | swings |  H   |  2B  |  3B  |   HR | ROE  | Outs |
+--------------+--------+------+------+------+------+------+------+
| No           |   4454 | 1236 |  208 |   24 |   88 |   71 | 3147 |
| Yes          |  13922 | 4530 |  905 |   79 |  512 |  162 | 9230 |
+--------------+--------+------+------+------+------+------+------+
ROE - reached on error

Rate stats for balls put in play
+--------------+--------+-------+-------+-------+--------------+
| inStrikeZone | swings |   AVG |   SLG | BABIP | HR_per_swing |
+--------------+--------+-------+-------+-------+--------------+
| No           |   4454 | 0.278 | 0.394 | 0.263 |        0.020 |
| Yes          |  13922 | 0.325 | 0.512 | 0.300 |        0.037 |
+--------------+--------+-------+-------+-------+--------------+
BABIP - (H-HR)/swings

The above results for balls in play are for the average batter in my sample, but, as they say, the average human being has one testicle and one breast. Vlad Guerrero is by no means an average player, so should any of this pertain to him? Well, let's drill down to the batter level, and pick out Vlad's performance:

Vlad Guerrero
+--------------+--------+------+------+-------+-------+
| inStrikeZone | swings | H    | HR   | AVG   | SLG   |
+--------------+--------+------+------+-------+-------+
| No           |     54 |   14 |    2 | 0.259 | 0.426 |
| Yes          |    102 |   41 |    4 | 0.402 | 0.637 |
+--------------+--------+------+------+-------+-------+

Here's an example:

Richie Sexson
+--------------+--------+------+------+-------+-------+
| inStrikeZone | swings | H    | HR   | AVG   | SLG   |
+--------------+--------+------+------+-------+-------+
| No           |     31 |   10 |    4 | 0.323 | 0.806 |
| Yes          |    101 |   23 |    7 | 0.228 | 0.455 |
+--------------+--------+------+------+-------+-------+

Final Thoughts

Strike zone judgment is not just a matter of laying off the bad ones to get more bases on balls. That is an important aspect, of course, but the better outcomes on balls in play on pitches that are in the strike zone, compared to pitches that are outside the zone, may be just as important.

The batter who swings at more strikes and fewer balls is helped in two ways: 1) he puts more of those balls in play and 2) the balls in play go for hits and extra-base hits more often. (These benefits are in addition to the better counts the batter gets by not swinging at balls.)

Ted Williams, one of the most disciplined hitters ever, thought the single most important aspect of hitting was "get[ting] a good pitch to hit." I like the positive way he phrased his point; he didn't say "don't swing at the bad ones." The emphasis was not on being passive, but rather swinging hard at a pitch you could handle, a pitch in what he called his "happy zone." Williams' "happy zone" actually referred to smaller areas within the strike zone (see picture). But, an obvious first step toward "getting a good pitch to hit" is to swing at strikes and not balls.

One last thought: It's interesting to consider what these results mean for DIPS theory, which holds that to a large degree pitchers have little control over how frequently balls in play go for hits. We saw above that BABIP for pitches out of the strike zone is .263, compared to .300 for pitches in the zone. If some pitchers were particularly skillful at getting batters to swing at balls outside the strike zone, they could show lower than expected BABIP.