Blog Review: Constructing a Test/ Retest System for Hitters by Driveline Baseball

Erick Mojica

B.S Kinesiology

January 17, 2019

I have decided to start writing more by sharing blog reviews of other baseball and health & fitness research, and this one is a piece from Driveline Baseball. As you may know, I follow Driveline heavily with their podcast and Twitter feed and think that they provide some of the greatest baseball content out there. Here’s a link to their latest blog.


Overall, they go into the importance of using a test and retest system to develop hitters. With so much technology available, the modern day coach has some amazing tools that help quantify what they are doing with their hitters.

The reason data collection is so important is because it gets us away from guessing and takes us to a point where we know whether or not our developmental plan is actually helping the player improve. But like anything else with numbers, what’s the point of measuring things if we don’t know what they mean?

If you’re a coach, player, or even a parent, it is important that you understand the metrics and their significance with hitting/ throwing mechanics. While it is valuable to know what the average is for a player you’re modeling after (say you want to be just like Mookie Betts), the reality of you putting up a Major Leaguer’s numbers is unrealistic.

Even if you’re comparing your swing metrics to someone else on your team, there is nothing more valuable than competing against yourself. If your pre-season training lasts 12 weeks, the most sought-after comparison should be what you performed on week 1 and what you get to on week 12.

batted ball data driveline
Driveline Baseball

Nonetheless, what you decide to measure has to be solely dependent on the tools that you have available. In the Driveline article above they talk about developing a system to track data. According to Driveline’s research, Bat Speed and Exit Velocity have the strongest correlations to hitting performance. With this in mind, using a radar gun and the Blast sensor device is a good start. A radar reading allows you to track two things: the hardest they can hit the ball and the average EV, ultimately measuring consistency. Using a Blast sensor device gives you swing characteristics for metrics like bat speed, swing plane, and attack angle.

With this process, you can then get into whatever hitting drills you believe will improve an individual’s swing outcome. If you work with several hitters and apply the same drills to everyone, there is a chance that only a few will see the benefit of what you made them do. This can make a world of difference to help all your hitters because you can then individualize their training program/ drill-work to work on their specific needs.

If you have a kinesiology and/or biomechanics background, you probably have a much deeper understanding that no one-person moves alike. The K-Vest is an amazing tool to measure movement and rotational velocity for the hips, torso, and arms during a swing or pitching motion. When you combine movement screens with data from a hitter’s swing, you can get more information about what the limitations are for that specific person.

A classic example is identifying a hitter who potentially has poor thoracic spine mobility. Let’s say that you’ve identified a postural deficiency in a hitter and then conduct some K-Vest data for a number of swings. You then find that they lose rotational velocity at the torso just milliseconds before making contact. You now know that this hitter needs to do one of or maybe both: work on their thoracic spine mobility through stretches and exercises or apply a medicine ball throwing program to increase force production. As a coach, you trust your instincts and apply the research that you’ve done to give your hitter the best training program that you can give them.

k vest driveline
Driveline Baseball

If you retest and don’t see improvement, then you go back to the drawing board to come up with a new routine and training program. And maybe you do that and see no improvement, but what matters most is that you are looking for ways to improve your hitter with actual data that you can measure.

For the scenario I just played out, you might come to find that this hitter actually has a tight hip and has a lumbo-pelvic rotation deficiency. Maybe he’s just weak and needs to get stronger through a strength and conditioning program. Who knows? But that’s the beauty of science. We test and retest until we find the results that we are ultimately seeking.

I think that it is extremely important for a coach or trainer to be able to say “I don’t know.” While it may not be the greatest strategy for client retention, at the very least you are being honest and willing to put in the work to figure out how you can help.

To be great coach, trainer, teacher, you have to be student of your craft. If you don’t know much, it’s up to you to do your research and acquire information. If you have experience and know what to look for, then why not become even greater and become a master at what you do?

This spring my 14 U team has been introduced to exit velocity testing and will soon be doing a variety of other data collection. Working on a budget, I fortunately have a parent bringing a radar gun to our weekly indoor practice.  I made a simple spreadsheet using Microsoft Excel to track each player’s progress as we prepare for our competitive season.

bc data 1bc data 2


The metrics that I have chosen to track are Average Exit Velocity (AEV), Peak Exit Velocity (PEV),  and currently searching for an efficient way to track Hips-to-Shoulder Separation (HSS), Bat Speed, and Attack Angle using a 2-Dimensional model (likely inaccurate but worth looking into).

  • AEV tells us how consistently hard they are making contact
  • PEV tells us the hardest ball that they’ve hit
  • HSS tells provides a visual for how well they rotate at the hips, torso, and arms
  • Bat Speed tells us how quickly they can whip the bat through the zone (we cannot validate true velocity but can measure time of a swing from start to finish)
  • Attack angle tells us at what degree they are making contact with a batted ball


There are definitely limitations to this system, primarily due to a lack of technology. Using an iPhone to record video and a Dartfish motion analysis software lacks the precision that a Blast Motion sensor can provide, but our system provides measures for Exit Velocity and motion analysis for all our hitters.

Although it is preferred to collect data with proven motion detectors, it is not impossible to analyze hitters with a smartphone. If you are new to biomechanics, you can learn a lot by using a motion analysis software app. I like using Dartfish because it allows you to measure angles and place timers with a slow motion video. If you have a basic understanding of good baseball swing characteristics, you can quickly pick up on some movement flaws/ efficiencies for a hitter you’re working with.










There’s a couple things to mindful about the video breakdown I made of J.D Martinez above. The timer is set at 00:00:00 sec from where I see him beginning to whip the bat through the zone. On top of that the video I used from YouTube Baseball Swingpedia was originally in slow motion, so there’s no way it took him 00:02:87 sec, but this is an example on how you can measure “bat speed” if you don’t have a motion sensor that can pick up the bat’s motion in MPH or MPS.

Also the angles shown in yellow were drawn from where I saw him make contact, set a 90° marker and subtracted from 157.1° to get his “attack angle” upon making contact, thus a measure of 67.1°. Because this model is not looking in a 3-Dimensional form, there are without a doubt flaws using a 2-Dimension to measure the true attack angle. We have to also take into account what angle the pitch was thrown at as well as the swing plane relative to time and space.

Here’s a link from Driveline Baseball on how they use Swing Plane to coach their hitters

Using Swing Plane to Coach Hitters: a Deeper Look

Like I said it’s not a perfect system without motion sensors, but if you have a consistent approach to looking at film and measure as accurately as you can, there are still ways you can obtain information on a swing.

Baseball Twitter is amazing and you can learn a lot by looking at a simple GIF. Driveline has a great team of biomechanics experts but there are a lot of other awesome people putting out content. Here’s a few of my favorite Twitter follows.

If you’re interested in learning more about hitting, Twitter is my number one recommendation. To all baseball players reading this, if you’re going to use time out of your day on social media, try spending it looking up baseball content.

The baseball community is highly active with tons of valuable information that you can engage with, and the more you research the more you learn. Comment and ask questions to guys like Jason Ochart, Craig Hyatt, and anyone else putting out content. Read other people’s responses and engage your mind into becoming a better baseball player.

Here’s some other great videos and Tweets that I have saved on my Twitter account!

Pitchers, read through this thread!!! ⬆️

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