First Pitch Swing Decision

An approach to provide insight on the first pitch.

First pitch begins an at-bat with Tableau Rasa, a Latin phrase that means clean slate. It begins with the pitcher and it ends with the batter. What the batter does with the pitch adds color to the slate that endures the entire at-bat.

The batter has a big decision – usually made as the first pitch approaches the plate - swing or take? That decision certainly has impact.

The batter can look for a specific pitch type in a specific location, and only swing if he sees what he is looking for (although he could be fooled). If he swings, the result is often excellent. On the other hand, when he doesn’t swing called strikes can happen, as can missed opportunities.

“Every good hitter when it comes to slugging the baseball looks for, and hunts for, and impacts the pitch they are looking for.” — Torey Lovullo

Alternatively, if the pitcher has poor command, the batter can set his mind on taking the pitch. Four possible advantages follow:

• The pitcher may fall behind in the count and groove a pitch down the center of the plate to get a strike.
• The batter and his teammates will see more pitches and can adjust their approaches at the plate. Also, more pitches can wear down a starting pitcher.
• The batter could be hit by pitch (average was about 2 in 1000 for first pitches in 2019/2020).
• Double plays are avoided when a runner is on first base.

How can the impact of that decision be measured? When the ball is put in play, wOBA indirectly measures the change in run expectancy. Two weaknesses in wOBA: it does not measure whether runs are actually scored and if the batter makes an out without advancing any runners, wOBA would be zero while actual run expectancy would be lower. Additional measures are needed.

That first pitch has many impacts on the entire at-bat. Two additional measures would look at the result of the entire PA.

• Actual runs scored are important. Let’s look at comparing RBIs per PA for first pitch swings and first pitch takes.
• Getting the most runs out of each swing is important. Let’s look at BABIP for first pitch swings compared to swings after first pitch takes.

How does the first pitch swing decision impact the Diamondbacks’ team?

In 2020, there was no impact on average BABIP. Whether or not the batter swung at the first pitch, BABIP for the PA was nearly the same (.282511 swing vs .282464 take per Baseball Reference).

In 2020, swinging at the first pitch increased RBIs per PA. RBIs per PA were .162 swing vs .096 take per Baseball Reference. Interestingly, the total of doubles & triples was lower with first pitch swing (.042 vs .054 per PA) while homers were higher with first pitch swing (.035 vs .023 per PA).

In 2020, first pitch takes impacted walks, strikeouts, double plays, and hits per PA. Walks increased 6.5%, while strikeouts increased 4% (a gain of 2.5%). Grounding into double plays fell by 0.9% (a gain). However hits per PA fell by 4.0%, effectively offsetting the gains. Data from Baseball Reference.

From the first three observations it seems that Diamondback team success is correlated to swinging at the first pitch.

Perhaps the type of pitch will reveal more insights. Let’s look at fastballs, breaking pitches, and off speed pitches. In 2020, for first pitch swings, Diamondback hitters were excellent against breaking balls; Their wOBA improved from .475 to .526. That strength was confirmed in Diamondback Batting - Do Pitch Types Matter?

However, for first pitch fastballs and off speed pitches, their results fell in 2020. As previously discussed on the AZ Snake Pit website, this season the Diamondbacks are expected to improve against fastballs. Details comparing 2019 and 2020 are in the following table.

First pitch swings, Diamondbacks. Data from Baseball Savant.

How does the first pitch swing decision impact Diamondback players?

Top level view.

It is different for each batter, but some batters have a better PA if they swing at the first pitch, and some have a better PA if they take the first pitch. Ketel Marte and Nick Ahmed hit better when they swung at the first pitch and have the additional distinction as grill masters (For a definition of grill master see Two Approaches to Scoring Runs). The following table shows two types of batters: those who were better when they swing at the first pitch and those who were better when they took the first pitch.

2020 season. Data from Baseball Reference.

Impact of pitch type.

Let’s look at fastballs, which seem to be an area the Diamondback players are working to improve. Does how often batters swing at first pitch fastballs correlate with wOBA? The following graph does not show any correlation. It does shows two paths to success: Ketel Marte’s wOBA of .584 with 19% swing rate, and David Peralta’s .488 with 29% swing rate.

2020 season. Data from Baseball Savant.

Ketel Marte’s hitting was pretty great the last two seasons - “Ketel Marte is a top-5 batter for all three skills (fire starter, fire builder, and grill master).” In spring training he reached an All-Star level of plate discipline. It will be fantastic to see him batting this season!

“It is absolutely jumping out at me, that he [Ketel Marte] is taking borderline pitches that are this far off the plate or this far on the plate that aren’t what he is looking for. That’s what impresses me more - the ones that are on the plate that he is letting go. And are called strikes because he is in one spot, one area, and it’s not there. That’s what makes him special right now.” — Torey Lovullo, 25 March 2021

It is very encouraging that of the 7 Diamondbacks whose wOBA against fastballs fell in 2020, only 2 had wOBAs below .353 when they swung at first pitch fastballs. That confirms that improvement against fastballs is achievable this season.

For first pitch swings, the batters with the highest wOBA against each type of pitch are shown in the following chart.

First pitch swings. 2020 season. Players with less than 5 pitches of one type excluded. Data from Baseball Savant.

Summary.

First pitch swing decisions had an impact. The Diamondbacks did well when they swung at the first pitch, perhaps because they often saw the pitch they were looking for. This season, that success will likely be repeated, especially for Ketel Marte.