Fastball Vertical Approach Angle
Vertical Approach Angle (VAA) isn’t a widely available metric. You can’t find it in the Statcast files from Baseball Savant. You never hear broadcast crews talk about it during baseball games. But it should be widely available and discussed, because it’s one of the most important pitching metrics available.
Vertical Approach Angle, in Layman’s Terms, is the angle in which the pitch crosses the plate. It’s basically the opposite of launch angle. It should go hand in hand with spin rate as to where a pitcher should primarily locate his fastball.
To measure VAA, the range of values goes from 0 to as large as -10 and below. A 0 VAA would be the flattest possible angle a pitch can enter the zone at, and the steeper the angle, the further the number gets from 0. Since technically it’s measured as a negative number, it can’t be referred to as “bigger”, so I will refer to it as “further from 0” to talk about steeper angles.
As you’d imagine, the pitches with more negative vertical break will typically have steeper VAA, signified by a larger negative number. These are the average Vertical Approach Angles for all pitches in our dataset:
VAA is primarily determined by 2 factors: extension and release height. A simple regression equation with those variables as inputs returns an R-Squared value of .945, a great predictor of VAA. More extension leads to a flatter VAA, and a higher release height shows a steeper approach angle.
For this analysis of the metric, finding each pitcher’s average VAA and making recommendations for improvement based on that doesn’t give the full picture. The ball doesn’t look or move the same at the top of zone compared to the bottom of the zone. It was easiest to split up the measurements into the top and bottom of the zone. The top of the zone consists of all fastballs between 3 and 4 feet off the ground, and -1 and 1 feet horizontally. The bottom of the zone is 1 to 2 feet off the ground, and the same measurements horizontally.
The golden question: Why does fastball Vertical Approach Angle matter?
The data is very clear, with a VAA closer to 0, fastballs should be focused higher in the zone.
This graph shows a very clear connection between a flatter VAA in the top of the zone and a higher whiff rate. Very similar to a high spin rate fastball, it has a rising effect, thus leading it to be much harder to get the bat to while at the top of the zone.
On the contrary, the bottom of the zone shows a steeper VAA yields far better results. Not only does whiff rate go up, ground ball rate and wOBA both show a steady trend in the right direction as well.
It’s pretty simple: if the fastball VAA is flatter, the primary location should be high in the zone. If the pitch has a steeper VAA, it should be located lower in the zone more often than not.
These numbers are helpful and all, but how do we know what’s flat? What’s an elite VAA at the top of the zone? Bottom? What is a bad VAA?
I took all of the data we have in our dataset, and created an Awful-Elite scale for both the top and bottom of the zone. These scales give context other than “over or under” the average. It shows where each of our pitcher’s rank among other pitchers across the nation, giving more explanation as to why results are the way they are.
The distribution of average pitcher VAA in the top and bottom of the zone both lead to a normal distribution, with a sample of 2,350 pitchers in both samples. These numbers are calculated with basic knowledge of the Normal Curve and Z-Scores.
This scale was re-run a number of times to deal with flaws in the sizing of each category. The original scale didn’t give an accurate representation of where players landed, nobody graded out in the “Elite” category, and there were a large number of players in the “below average” category. So I tuned the scale to create a normal distribution for both zones, giving a better representation of where players are compared to their peers.
Importance, explained. Context, established. So how can these numbers help a baseball program? Finding each pitcher’s average VAA in both zones was the first step. From there, it was about finding and analyzing important metrics to determine how each pitcher was performing relative to their VAA.
One very nice point of this metric is sample size is mostly irrelevant when finding a player’s VAA. Whether he throws 2 or 200 pitches in each zone, the average VAA doesn’t need a large sample to even out in order to give an accurate view.
This chart was the one created to give a brief overview of where our guys are, plus an easy metric to analyze, whiff rate, to show how well each pitcher is missing bats in each zone.
There are a few strong examples within our team that could be using their fastballs more effectively. In these datasets, I added wOBA to give more context about the results if the ball was put in play. Whiff rates are nice, but if the ball is crushed every time it’s put in play, whiff rate becomes less useful.
This pitcher is throwing a very similar number of pitches high and low in the zone, but he has the best high zone VAA on the team. His arm slot is close to ¾, and his fastball plays very well up. His whiff rate nearly doubles when he throws high.
On the flip side, this is a pitcher who’s fastball often times gets knocked around the yard. Of the sample of 2,350 pitchers, his fastball had the 92nd best low zone VAA, top 4% in the dataset. His wOBA nearly quadruples high in the zone. Yet, he’s throwing over twice as many fastball high in the zone.
This would be a simple fix that could drastically improve the effectiveness of this pitcher’s fastball. Focusing on the low part of the zone would induce substantially more ground balls and more whiffs than filling up the top of the zone.
There are more improvements that could be made within our pitching staff, these are just focusing on the most glaring sores in this dataset.
VAA should be kept in mind both when considering how to develop pitchers, but also with in game decisions. If a double play is needed, a pitcher with a steep VAA would be a more logical choice. High strikeout guy at the plate that can’t layoff the chest-high fastball? Probably look for a flatter VAA to come out of the bullpen.
The next step of this project is to analyze VAA on breaking balls. Does a steeper VAA induce a more effective curveball? What offspeed pitches work best with a flatter fastball VAA? Does VAA matter when throwing a changeup? The questions are endless. With such a strong connection between VAA and fastballs, I can’t wait to dig into what the connection between VAA and offspeed pitches will be.
VAA is a very important metric, but it’s not the end all be all location metric. It’s still very important to mix up locations to avoid becoming predictable and keep hitters guessing. Utilizing this metric effectively will hopefully become a mainstay within our player development program in the near future.
