The science of scouting: A biomechanical look at Danny Hultzen

The Seattle Mariners shocked the baseball blogosphere when they chose Danny Hultzen over Anthony Rendon in the free agent draft this week. In subsequent radio interviews in the Seattle area, Jack Zduriencik said the team’s had eyes on Hultzen for years, and that they put top scout Tom McNamara on Hultzen all year at the University of Virginia. Hultzen’s stats are no joke, but then again, neither are third pick Trevor Bauer’s—my preferred pitcher in the 2011 Major League Baseball Draft. (203 strikeouts in 136 innings pitched? I can’t wait to see Bauer in the big show.)

Ahem. This article is about Danny Hultzen and not my personal man-crush on Trevor Bauer, so let’s get back to it.

Scouting Danny Hultzen – Using A Scientific Approach

There are many, many articles out there talking about Hultzen’s 90-94 mph fastball, passable slider, plus-rated changeup, and great character, so I’m not going to talk about these nebulous grades. I’ll leave the 20-80 scouting scale to those who actually hold scouting jobs. Nor am I going to talk about his arm action, ball release, and follow-through phases based on my personal preferences. Rather, we will use crude planar two-dimensional biomechanical analysis techniques to analyze Hultzen’s delivery, using what video we can find on the Internet. The video I’ll use is this series of clips shot by, available on YouTube:

A FEW WORDS OF CAUTION: This video, like many others, is shot from the side at a slight angle. Ideally, we’d have a video that is shot to present the pitcher perfectly from the side, in line with third base, first base, and the pitching rubber. Additionally, the video quality here is not great, and is shot at 25-30 fps. For reasonably accurate planar static kinematic values, we need a 90-degree shot, with 200+ frames per second video quality, and a stable camera. We’ll do what we can, with this note that parallax error and a low sampling rate will both play significant roles in our analysis.

This a perfect reason why MLB teams should have a detailed video library of all the pitchers and hitters they are interested in—shot with a checklist of quality markers for analysis, using consumer-grade high-speed cameras.

Metrics for Analysis

The metrics with which we’ll grade Danny Hultzen can all be found in various baseball research papers and represent elite (MLB) pitchers who have been biomechanically analyzed by various researchers and groups, and who have generally been injury-free. No guarantees can be made, as the participants in studies are subject to health privacy laws, and various selection biases may have been introduced. However, these metrics are all based on scientific research and are not invented by someone with personal bias. They are also not qualitative—there will be no measurement of a “fast arm action,” a definition that might mean many different things to many different people.

Metrics for today:

-Maximum Knee Height (absolute and relative to height)
-Degrees of Shoulder Abduction at Foot Contact
-Degrees of Lead Knee Angle at Foot Contact
-Stride Length at Foot Contact (absolute and relative to height)
-Degrees of Maximum External Rotation (MER)
-Degrees of Lead Hip Flexion at Ball Release

Maximum Knee Height

Nolan Ryan once said that the higher he lifted his glove leg, the harder he could throw. While this statement might not have a lot of absolute merit to contributing to fastball velocity, research does back up the concept of a fairly large maximum knee height being prevalent amongst the top tier of baseball pitchers.


Danny Hultzen’s maximum lead knee height is approximately 55.25 inches, good for 73.6 percent of his standing height of 75 inches (error unknown). Most research indicates that the best pitchers have a maximum knee height between 60-70 percent of their standing height.

Stride Foot Contact Metrics

At foot contact, there’s a lot of stuff going on that we’re measuring. Hultzen’s…

  • Shoulder Abduction (think: height of elbow) is about 93 degrees (error unknown). Research suggests elite pitchers are generally between 80-100 degrees at this phase of the delivery.
  • Lead Knee Angle is about 139 degrees (error unknown). Research suggests elite pitchers are generally between 125-140 degrees at this phase of the delivery.
  • Stride Length is about 42.88 inches or 57 percent of his standing height. (error unknown). Research suggests elite pitchers generally stride 75-90 percent of their standing height.

Maximum External Rotation (MER)

Maximum External Rotation (MER) is actually a pretty big misnomer; it describes the angle at which the forearm “lays back” during the pitching delivery. This is due to a rapid turn of the shoulders as the inertial mass of the baseball pushes the hand and forearm back. The problem with the term is that “shoulder external rotation” describes the humerus rotating backwards, while in reality scapular tilt is providing a significant amount of the “external rotation” during this phase. It is, therefore, multiple components being measured as a single thing. Scapular tilt is hard to measure without markers on the scapula and a bridge connecting them, and so researchers have just grouped these variables together; it’s stuck ever since. Evidence suggests that scapular tilt varies between overhead throwing athletes, so comparing MER between athletes may introduce a gross error based on anatomical and congenital differences between the two.

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But enough naysaying and biomechanical nerd-jargon. Hultzen’s MER is about 197 degrees (error unknown) based on the best video frame I could find that showed the maximum “layback” possible. Research suggests that elite pitchers tend to range from 170-190 degrees of “MER” throughout the delivery.


A few more words on MER: How MER is achieved, and is not controlled in these studies. The rate at which the forearm enters “maximum external rotation” (which I will now call “maximum forearm layback,” or MFL) is vitally important when trying to solve for kinetic derivations like joint torque, which is ultimately responsible for the total and peak stressors on the body’s structures. MFL itself tells us just one thing out of many factors that make up the important parts of the just that phase of the delivery—rate of MFL (rMFL) is very important as well, and this cannot be determined using standard-definition 30 frames per second video.

Hip Flexion

At ball release, Hultzen’s lead hip flexion is about 100 degrees (error unknown). Research suggests that elite pitchers tend to be between 92-115 degrees of hip flexion at ball release.


Wrapping it Up

By all the basic research standards that we chose (except for stride length), Danny Hultzen has the biomechanical markers of an elite pitcher. A coach might suggest that Hultzen increase his stride length to increase his fastball velocity, but no research has correlated these two specific variables, regardless of what popular Internet pitching coaches will tell you.

This article should help shine on a light on what is necessary to maintain even a basic video library for crude biomechanical analysis techniques, and illustrate the limitations of planar biomechanical analysis of static kinematic variables. A three-dimensional approach using synchronized high-speed cameras is a far better tool to evaluate the kinematics and kinetics of baseball pitchers, to assess red flags in a pitcher’s delivery, to help unlock fastball velocity and increase durability. As I said in my first article for The Hardball Times, Driveline Baseball is working hard at developing a low-cost mobile solution that could easily be implemented in a team’s stadium like PITCHf/x.

References & Resources
Thanks to for providing the YouTube video we used in today’s analysis.

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Kyle owns Driveline Baseball and Driveline Biomechanics Research, and has authored The Dynamic Pitcher, a comprehensive book and video set dedicated to developing elite youth baseball pitchers. He is also a consultant for an MLB team and a major Division-I college program. Follow him on Twitter @drivelinebases or email him here.
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Jeffrey Gross
Jeffrey Gross

This is super cool stuff. Way over my head, but super cool


wow, awesome stuff.

Mike Newman
Mike Newman

Extremely interesting piece. In this case, the biomechanics match the scouting as wrote him up as a top flight starter in the end. If you ever need raw video to manipulate like the Hultzen vid, please let me know. The video uploaded to YouTube has already been converted and uploaded and it definitely dings quality.

Kyle Boddy
Kyle Boddy

Thanks, everyone. Raw video is definitely better, but it doesn’t improve the analysis all that much. The primary issues are the sampling (frame) rate and the angles at which the video is shot.

For more, check out my website!


This is very cool! From looking at the video from behind home plate, his stride is slightly towards the first base side. I would think that affects your measurements from the side video relating to his stride length (and knee angle?). And is this angle of his stride (relative to straight on) another metric that has significance?