Back in September 2019 when we started team practice, we typically had our Rapsodo Hitting unit set up during practice, as well as having our hitters use a Blast Motion bat sensor. Due to the quick pace of batting practice, waiting for Rapsodo to load the data on the screen between pitches is time consuming and difficult to see from the batters box. We started using a white board to chart exit velocities over 90 mph to create some competition and not just have the Rapsodo go to waste. This definitely helped in getting the players more into it, and even got the attention of the pitching staff one day as they all came over and egged the hitters on. But beyond the competition piece, we felt like we still were not getting nearly as much value out of Hitting Rapsodo as we could be.
We came up with the idea to start pairing the Blast Motion data with the Rapsodo batted ball data. We wanted to see if Blast Motion could help paint a better picture as to why certain balls were being hit harder than others.
With the help of our managers and analytics team, we were able to keep track of every swing. The chart below is a snapshot of the chart we would use during BP. By writing down the exit velocity of every swing, the exit velo's could then be used as reference points for us to go into Rapsodo and copy and paste the data into the Blast Motion CSV file.
As you can imagine, not every round ends up only being 5 swings and there can be misreads, so you need to pay close attention to the Blast swing number, and the swing and coinciding EV on the sheet.
Below is an example of a heat map we were able to make as a result of pairing the two technologies. The inner 3x3 represents the strike zone from the catcher’s perspective. The top number within each cell is the average for that particular metric, while the bottom number represents the sample size in that part of the zone. (S/o Indians RHP Prospect and former Duke Kevin Kelly for helping create this.)
Some notes about these charts: they should be taken with a grain of salt because 1) Blast is in no way the end all, be all of hitting; 2) Rapsodo does not capture point of contact which has a large effect on many of these numbers (ie. Bat Speed and Attack Angle increases the further out in front of the plate contact is made); 3) we would like to see a sample size of at least 30 swings per cell to make this more meaningful; 4) many of these swings were off of BP or front toss, hence the fairly consistent exit velocities throughout the zone; and 5) Rapsodo has occasional misreads for both zone location and batted ball events. Like I said, there's a lot to consider.
How Can We Use These Charts?
So now for the part that actually matters, how we are putting these charts to use. Rapsodo lost over a month's worth of our data which obviously we could have used to make better heat maps. But theoretically, let's say the heat maps are 100% accurate. I feel like the charts can be used both as a coaching tool in addition to helping individualize an in-game approach for our hitters. For example, Vertical Bat Angle(VBA) means very little to me in the sense of an overall average because it changes drastically throughout the zone. Identifying that on the heat maps could be an extremely helpful coaching tool as a means of correcting posture and adjustability. I will touch on this again in a couple paragraphs.
Anthony Shattell (@soxmoneyball on Twitter) has brought up many interesting points to me about Blast Motion. Something he has put together is a “Good Swing Percentage,” as he defines on Blast Motion as a swing that has all of the following traits: 90% or higher of the hitter’s maximum bat speed, between 6 and 20 degree attack angle, and 60% or higher on plane efficiency. He has also calculated a way to find pitch location solely based on Blast Motion data. A hitter could potentially develop his approach around the part of the zone that has the highest “Good Swing Percentage.” In the case below, laying off the low and in pitch could be most beneficial due to having a good swing percentage of just 6%.
Referring back to the 6 heat maps, visualizing the (VBA) is important. The hitter’s heat map for the VBA in this case is good, we are looking for a gradual change in color as the VBA should be steepest (more negative) on the low and inner half on a right-handed batter and gradually get closer to zero at the upper parts of the zone. A hitter who does not do this well is a possible sign of poor posture and connection at impact. Shatell refers to posture as spine angle, and calculates it on Blast Motion with the following equation:
Spine Angle = 90 – (Connection at Impact + Vertical Bat Angle)
The process for collecting all of this data is time consuming and with only one sensor, takes a while to make meaning of it all. However, we feel like it has potential to be very useful moving forward as we continue to collect data off more game-like pitches.
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