Update 6/1/18: Clayton Kershaw will get an MRI after experiencing back tightening on Thursdays game against the Phillies. Kershaw returned for his first game back from the DL due to left biceps tendonitis since May 1.

August 21, 2017: This is not new to him. In 2012, he had right hip impingement. In 2014, he had a strained left teres major muscle. In 2016, a lower back injury in which he had an epidural.

So what's going on with Clayton. A few things I was able to pick up from watching him pitch, walk, move, and jog (mainly during his warm-up routine).

Limited left hip extension - because his hip doesn't extend backwards, it will and does limit the stride portion of his pitching phase (at the end when his body rotates and he is facing the batter). How does he compensate? With a little too much of a left trunk lean.
Limited left hip internal rotation - because he doesn't have this motion, during hip windup he will, and does, excessively rotate through his spine. You can see this as he walks and especially when he is going up stairs. He rotates to his right when stepping up with his left leg. His limited hip rotation also creates excessive torque at his knee which could be causing him so mild knee problems that could escalate to a ligament tear.
Limited left hip flexion - Watching him bend down and pick up a ball, he is quick to go over his right hip and avoid his left hip, most likely due to limited flexibility with his hip bending movement. This is also showing up with a left pelvic hike. (When he does knee highs in warmups, watch him lose balance when lifting his left knee. This is because he has limited motion and is harder to perform for him).
Left Leg versus abdominal weakness - Watching him jog, when on that left leg, you can detect some instability which shows up as extra rotation when on the left leg. You can notice his body rotates excessively to the right, meaning either he has some weakness in the left leg which is not being a good base to his pelvis and spine or abdominal weakness in one of his oblique muscles. This is a problem because his left leg is where he generates his power during pitching. If he's got weakness in those areas, he will compensate with overuse of his back muscles.

So what's going on with Kershaw. Something in his left leg is restricting and weak causing excessive spinal compensation that will continue giving him back problems no matter how many cortisone shots or surgeries he gets. He has had an amazing career to date. Let's just see if he can manage these injuries and get through the rest. Shockingly, his compensatory problems have not really affected his performance, just kept him on the DL longer than the Dodgers liking. He does have a great warm up routine, although he should be incorporating some hip internal rotation range of motion (I only saw external rotation). Because of the snowball effect, I only see his problems getting worse unless he has these compensations addressed.

The Injury Analyst is a blog dedicated to not only explaining injuries that have occurred, but predicting and highlighting future injury risks for professional athletes. You can email us at info@jamsportsandspine.com

Note: I have not seen the subject of this article personally in clinic, rather all views and opinions of the author have been made based off of video footage of the athlete. This article is not meant as a diagnosis or a treatment plan.