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MLB Offseason Injury Report: Breaking Down A.J. Puk… or Is A.J. Puk Breaking Down?

Nic Civale is a Doctor of Physical Therapy and former NCAA Division I Baseball player. He combines his knowledge of anatomy and physiology with that of baseball mechanics to provide expectations for players who will be rehabbing this offseason. Utilize The Offseason Injury Report to start your planning for 2021 drafts and keeper decisions. Today he looks to diagnose the injury issues of A.J. Puk.

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MLB Offseason Injury Report: A.J. Puk

A.J. Puk has everything in his physical stature to draw the eye of any baseball fan. He’s a towering giant and throws upper 90’s heat from the left side.

Puk’s 2019 season gave us his Major League debut and an 11-inning sneak peek at his talents against the world’s best… as well as the Detroit Tigers. He did not start any games on the mound but was used out of the bullpen, amassing 13 strikeouts along with 5 walks. The majority of his arsenal was comprised of 4 seamers and sliders, making up nearly 90% of all of his pitches. The two pitches can reach speeds of 99 and 91 miles per hour, respectively

In his 13 strikeouts from 2019, he hit spots all around the strike zone, utilizing both his 4-seam and his slider effectively. The fastball up/slider away combo to lefties looked especially challenging for hitters. Puk has amazing potential, and it doesn’t take much research or analysis to realize this. One of, if not the only, thing that could slow him down is his proclivity for ending up on the IL.

Previous Injuries

Every time the big lefty was getting close to his return to playing time in 2020, he experienced a setback and was shut down. He was ultimately sidelined for good in September when he had rotator cuff and labrum debridement surgery. Debridement is used to clean up an area from fragments of tissue that are either loose or fraying. They can cause pain or limit the range of motion of the joint. There is no reattaching or restructuring of injured tissue that takes place, so recovery times are often speedy. In a vacuum, a debridement surgery is nothing to be particularly concerned about for a pitcher, especially if there aren’t any reported setbacks.

The concern to me is that the shoulder injury emerged after a long recovery from TJS that was performed in April of 2018. Everything seemed to be going well, initially. A.J. Puk had made his way all the way up to the majors and was hitting the velocities expected up him. But after 11 Major League innings, and a full offseason of rest, Puk was never able to get going in 2020. Shoulder injuries often follow elbow injuries when the player is actively or subconsciously limiting the strain put on the elbow. It’s possible Puk was trying to limit the strain on the elbow and inadvertently redirecting it to the shoulder. It’s also possible the tissue in the shoulder had been injured for years, and the pain had finally surfaced.

A.J. Puk’s Mechanics

When trying to figure the etiology of the injury, there are a few things we must consider. As a physical therapist who doesn’t work with Puk directly as a patient, I can’t rely on a shoulder examination or palpation techniques to discover where weaknesses, limitations or pain exists. What I can do is consider pitching mechanics and previous injury.

Taller pitchers with longer limbs often times have difficulty repeating a delivery and can benefit from a shorter arm circle prior to release of the ball, ie. Lucas Giolito circa 2018 vs 2020. Puk’s arm circle is not abbreviated and may even be a bit longer than most. Going through Puk’s pitching mechanics, though, was quite revealing in a good way. Using’s film room site, I took a look at a few major milestones in the process of delivering a pitch.

  1. Timing of hand/glove separation
  2. Hand/elbow position when the front foot lands
  3. Location of stride foot when striking the ground
  4. Momentum of body following release
  5. Pelvic/hip rotation throughout the entire delivery

DISCLAIMER – The short analysis here is that Puk does things a bit differently, but ultimately, he has consistent mechanics, especially for a taller pitcher. For further analysis of this concept, take a look at the biomechanics deep dive below.


Puk is actually very consistent in his ability to separate hand from glove in the same moment of nearly every delivery. He also manages to reach, or get close to reaching full external rotation of the left shoulder by the time his front foot lands. External rotation of the shoulder is what your shoulder does when you reach back behind your head. It’s often the position pitchers are in on their baseball cards, when you’re wondering how their arms got to be in that seemingly impossible, lay-back position.

My first reaction to analyzing Puk’s mechanics was that I thought he tended to break his hands a bit late for my liking. I’m no pitching coach, but mechanically speaking, there is a lot of activity that needs to happen from the time a pitcher breaks their hands to the time their front foot hits the ground.

When a pitcher breaks his hands late, they risk needing to hurry the rest of their mechanics to reach maximal external rotation by the time their stride foot hits the ground (or very very soon after that.) So the only options following a late hand break are, hurry your mechanics to catch up by the time your stride foot hits, or risk putting increased strain on your elbow and shoulder by asking them to reach their maximal external rotation after the front foot lands.  This problem is amplified when your limbs are longer, like Puk’s.

Puk does something interesting here though; he takes advantage of his excellent balance, and long legs to really maximize the duration of his stride. He successfully makes up for a slightly late hand/glove separation by prolonging his stride time. As he hits the ground with his front (right) leg, he is on top of the ball and finishes the delivery with extremely consistent and controlled momentum towards home plate.

Ultimately, in order to reduce torque on the elbow and shoulder, the body needs to maximize its function and efficiency from the ground up. That’s where the 5th milestone, pelvic/hip rotation, comes in. Puk tends to stride towards the first base side of the mound. He simultaneously uses his back muscles effectively to draw his shoulder blades (scapulae) together to create maximal energy potential as he brings his arm forward. This creates a position of maximal capability to produce high-velocity pitches. It also creates a deceptive angle, as the ball is released from the left side of home plate at his release point, and goes away from lefty hitters and towards righties. This type of stride is definitely not unique to Puk, but anyone who does set themselves up to pitch cross-body needs to have excellent hip mobility and hip dynamic stability.

If you think of Puk’s right leg as an axis, he needs to translate all the power he generates from pushing off the mound and direct it towards his target. Since his right leg lands slightly to the left, he has to rotate around that hip to re-direct the momentum back towards home plate. This is something people have done for their entire careers without issue, but it requires that right hip to take on a lot of responsibility.

It is difficult to make the connection between this demand on the hips and any type of compensation injury to the arm. Again, we’d need some data on Puk’s hip range of motion and stability. Let’s hope it never happens, but if Puk ever shows up on the IL with right hip pain, then I will be very concerned.


After all this analysis, there is no definite conclusion as to why Puk’s shoulder injury occurred. It could have been a chronic injury that got too painful, a result of limiting his elbow’s role in the delivery, or maybe an overcompensation from the shoulder due to limited hip rotation. Overall, the shoulder will likely heal completely from that type of surgery, and there should be no major changes to his mechanics.

Based on all of this information, combined with his immense talent and physical gifts, I’m very excited for Puk’s fantasy value…but not this year. Yes, the A’s have committed to the idea that Puk is still expected to be a starting pitcher. In the long run, I believe he has the tools and the organizational support to do this. He has the upside of a true ace, but his floor remains lofty as a Josh Hader-like reliever. But Oakland would be taking a massive risk on their top prospect if they decided to unleash him this year. We’re all wondering who’s going to get to 200 innings pitched this year, but A.J. Puk has only 194.1 innings in his professional career since he was drafted in 2016.

If I was to project a full-season body of work for Puk, I wouldn’t even optimistically peg him for anything over his career-high in innings (125 in 2017). His ERA,  K/9 and BB/9 have remained relatively consistent from his time at U of Florida all the way up to the majors, and there’s no reason to think that’ll change. Additionally, the Athletics surely hope and expect to make the postseason again this year, and would like to have their young, potential ace ready for October.


My pre-spring-training projection for Puk would be this;

80 IP, 95K, 35BB, 3.78 ERA, 1.24 WHIP

If you like comps, it’s not all that different from a rookie Julio Urias, and I think that’s how we have to treat him this year. Spring Training can be helpful in evaluating Puk. I don’t think his stock would rise significantly even if he pitched well and started games; Oakland will limit his innings no matter what. But any nagging injuries or early exits turns him into a do not draft for me- at least this year. If he has a healthy season and pitches with consistent mechanics and velocity, watch out 2022! Cuz AJ Puk will be rising quickly.

If you haven’t already, you HAVE to check out Eric Cross’s work here in the top 300 prospects list for MLB. Unbelievably thoughtful analysis and lots of hard work goes into it. Treat yo-self!

Top-400 Fantasy Baseball Prospects For Dynasty Leagues: December 2021

For more great rankings, strategy, and analysis check out the 2021 FantraxHQ Fantasy Baseball Draft Kit. We’ll be adding more content from now right up until Opening Day!

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  1. Dennis the Menace says

    EXCELLENT write up.
    Can you do Brendan McKay next?

    1. Nic Civale says

      Thanks! Yeah I’ll get on that. I’m not sure if it will be the very next article, but I’ll get something out before the season. Not quite sure what information is available on his rehab and surgeries be I’ll dig in as much as I can

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