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Mark Prior's Pitching Mechanics
A Comparative Analysis


Few major league baseball pitchers have been the subject of more debate than Mark Prior. I know that Carlos Gomez has discussed Mark Prior's pitching mechanics on The Hardball Times on at least one occasion. I would like to offer a different perspective on Mark Prior's pitching mechanics and an alternate explanation for his arm problems.

When You Assume...

One thing I do for a living is work as a troubleshooter of complex computer systems. A lesson I have learned repeatedly (and sometimes the hard way) over the years is that one thing that will get in the way of your understanding what is actually going on in a system is the assumptions you make.

When Mark Prior, his coaches, and others compare his current mechanics to the mechanics he used in the past and look for things that have changed over the years, they are implicitly assuming that his mechanics were good in the past and that the root cause of his problems is that his mechanics have changed over time. That seems like a reasonable assumption to make, given that when he first came up Mark Prior was widely and loudly trumpeted as having perfect pitching mechanics.

However, over the years various credible people (e.g. Steve Stone) have questioned the actual quality of Mark Prior's pitching mechanics in light of his injury history. As a result, I recently decided to compare Mark Prior's pitching mechanics to the pitching mechanics of a couple of successful and relatively durable pitchers and look for differences between their pitching mechanics. The comparison pitchers I chose were Greg Maddux and Nolan Ryan.

I believe I have found some differences that may help to explain Mark Prior's injury problems and that suggest that Mark Prior's pitching mechanics were never as good as they were touted to be.

Comparison: Mark Prior & Greg Maddux

First, let me compare Mark Prior's pitching mechanics to those of Greg Maddux, one of the most successful, and durable, pitchers of recent history. The clip of Greg Maddux that I have chosen is one from when Maddux was 19 years old and was at roughly the same point in his career as Mark Prior. If you compare the two clips, you will see two general areas of difference: lower body action and arm action.

Comparison - Mark Prior vs. Greg Maddux Pitching Mechanics

Mark Prior vs. Greg Maddux

Mark Prior and Greg Maddux do have quite different lower body actions. Mark Prior's lower body action is relatively more linear; during his stride his Glove Side (GS) foot moves pretty much directly toward the target. In contrast, Greg Maddux's lower body action is more rotational; rather than striding directly toward the target, Greg Maddux sweeps his leg out toward Third Base before landing with it pointing at the target. Some have suggested that this difference means that Mark Prior isn't as efficient as Greg Maddux. While this may be true, I don't think it's especially significant. For one thing, Mark Prior is much bigger than Greg Maddux, so he can stand to be slightly less efficient with his mechanics. Second, if you look at Frame 30/101, you will see that Mark Prior and Greg Maddux achieve similar levels of hip/shoulder separation, which is the primary source of a pitcher's power.

Comparison - Mark Prior vs. Greg Maddux

Mark Prior vs. Greg Maddux

Mark Prior and Greg Maddux also have very different arm actions, and because what we are talking about are Mark Prior's arm problems, I think this is a much more significant difference. As you watch the two clips, watch what their Pitching Arm Side (PAS) elbows do. After he breaks his hands, Mark Prior's PAS elbow quickly gets quite high; it goes above and behind the level of his shoulders. In contrast, after he breaks his hands Greg Maddux's PAS elbow gets low and then stays low. This difference is extremely obvious in Frame 28/097 and Frame 29/099. Also note that in Frame 30/101, when Mark Prior and Greg Maddux are both in the high-cocked position, Mark Prior's PAS elbow is well above the level of his shoulders while Greg Maddux's PAS elbow is well below the level of his shoulders.

I believe this difference is significant because it is a well-established fact that people like plumbers, pipefitters, sheet metal workers, and others who constantly work with their arms above their heads are much more vulnerable to shoulder problems than is the general population.

Comparison: Mark Prior & Nolan Ryan

Some people will say it's not fair to compare Mark Prior to Greg Maddux since Mark Prior is a power pitcher and Greg Maddux is a finesse pitcher. As a result, let me compare Mark Prior's pitching mechanics to those of one of the ultimate power pitchers: Nolan Ryan. Nolan Ryan threw even harder than Mark Prior but was relatively much more durable.

Comparison - Mark Prior vs. Nolan Ryan

Mark Prior vs. Nolan Ryan

If you compare the two clips, you will see that Mark Prior and Nolan Ryan have lower body actions that are relatively similar; while their leg lifts are different, they both have a fairly linear move toward the plate with their GS feet. What is different about the two clips is their arm action. Mark Prior and Nolan Ryan both break their hands in similar places and in similar ways. The difference is that after breaking his hands Mark Prior breaks his elbows vertically while Nolan Ryan breaks his elbows more horizontally back toward First Base. As a result, by Frame 28/10 Mark Prior's PAS elbow is above and behind the level of his shoulders while Nolan Ryan's PAS elbow is behind his shoulders but significantly lower. More importantly, by Frame 30/14 Nolan Ryan's PAS elbow has dropped to below the level of his shoulders while Mark Prior's PAS elbow has stayed above the level of his shoulders. As with Greg Maddux, I think this is a significant difference.

Mark Prior In Detail

So that I am perfectly clear about the problems I see in Mark Prior's pitching mechanics, let me pull out a few frames from the clip above and discuss them in detail.

Mark Prior

Mark Prior - Frame 26

Frame 26 is where Mark Prior starts to go off the rails. It's not completely obvious, but what Mark Prior is doing is leading his hand break and arm swing with his Pitching Arm Side (PAS) elbow. Some people call this breaking the hands with the elbows. The result is that Mark Prior's PAS elbow will end up much higher than is normal (or safe). That will put him in a position to damage both his elbow and his shoulder.

Mark Prior

Mark Prior - Frame 27

In Frame 27 you can see how Mark Prior has continued his arm swing and you can see how his PAS elbow has continued to come up. The PAS elbows of Greg Maddux, Nolan Ryan, Roger Clemens, Randy Johnson, and many other great (and durable) pitchers never get this high during their arm swing.

Mark Prior

Mark Prior - Frame 28

In Frame 28, Mark Prior is at a position that I call the Inverted W. Notice how his PAS elbow is both above and behind his shoulders and his PAS forearm is hanging down nearly vertically beneath it. This position isn't damaging in and of itself. However, by coming to this position, Mark Prior is ensuring that his PAS arm will not be in the proper position at the moment his shoulders start to turn. Instead, it will be "late". As with pitchers like Kerry Wood, who have similar timing problems (e.g. rushing), this dramatically increases the load on both the elbow and the shoulder.

Mark Prior

Mark Prior - Frame 29

In Frame 29, Mark Prior is landing sharply on his GS heel, but that's the least of his problems. Because his GS heel is planting, we know that Mark Prior's shoulders are just about to start rotating. The problem is that Mark Prior's PAS arm isn't ready. Instead, it's extremely late. Notice how his PAS forearm is not yet horizontal. In a pitcher like Greg Maddux, his PAS forearm is much closer to vertical (e.g. pointed upwards and near the high cocked position) at this moment. Mark Prior's PAS elbow is also extremely, and unusually, high at this moment. I believe that this places an extraordinary level of stress on both the Rotator Cuff and the Labrum.

Mark Prior

Mark Prior - Frame 30

In Frame 30, Mark Prior's shoulders have just started to turn. Notice that the word "Trojans" on his chest has shifted to the right as his hips have started pulling his shoulders around. However, at this moment Mark Prior's PAS elbow is still extremely high. It is well above the level of his shoulders in a position of Hyperabduction. Evidence from other fields suggests that that this can lead to impingement and other problems in the shoulder.


A wide variety of explanations have been proposed over the years to explain Mark Prior's injury problems. These explanations include poor conditioning, inefficient mechanics, the effects of other injuries, and gradual changes in Mark Prior's pitching mechanics over time. While each of these explanations has its merits, I think the differences that I have established between the pitching mechanics of Mark Prior and the pitching mechanics of Greg Maddux and Nolan Ryan suggest that a simpler explanation may be the correct one; that Mark Prior's pitching mechanics were never as good as people thought they were, and that Mark Prior's pitching mechanics are largely responsible for his injury problems. As a result, I would not be surprised if the fans of the San Diego Padres find Mark Prior to be as big of a disappointment as the fans of the Chicago Cubs have found him to be.

3.12.2009 Update

I recently completed a piece that addresses the question of Mark Prior's perfect pitching mechanics.

3.15.2009 Update

I was the first person to express concerns about Mark Prior's shoulder back in late 2005 in my photographic analysis of Mark Prior's pitching mechanics PDF.

6.30.2010 UPDATE

It turns out that Mark Prior is making another attempt at a comeback, so I put together a piece that discusses Mark Prior's New Pitching Mechanics.

About The Author

Chris O'Leary never played baseball beyond grade school due to a shoulder injury suffered due to poor pitching mechanics. As a result, he is focused on ensuring that what happened to him doesn't happen to anybody else. The Epidemic is one way he hopes to achieve that goal.

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