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In a season that has been beset by pitcher injuries, the loss of the game's most electrifying ace, Jose Fernandez, was the straw that broke the collective heart of the baseball universe. How did it come to this?

One of the missions of Raising Aces is to explain the why and the how behind pitcher performance. There are known reasons why a pitcher might be missing his spots, and we understand how he creates movement on his pitches. Unfortunately, we’re far from identifying concrete truths about why and how a given pitcher gets seriously injured.

By day I’m a mild-mannered educator, and right now we’re knee-deep in finals preparation. One of the most useful strategies that I employ with the students is “to know what you don't know.” The method requires an honest analysis of one's strengths and weaknesses, with the goal of isolating potential problem areas in order to optimize the learning process. When we bring this method to bear on the baseball world, it’s important that we appreciate and accept the current state of injury evaluation, in which there are far more questions than answers.

It's human nature to attempt to isolate a singular cause when something goes wrong, but science rarely affords us the convenience of simplicity, and the profile of a professional pitcher is riddled with intertwined risk factors that can conspire to take him off the mound. The analytical community is still trying to understand these elements on an individual basis, and the issue is further complicated by the chain-linked nature of the variables at play. Very rarely is the explanation obvious, and mechanics are just part of the picture.

Let's take a look at some of the pieces in the injury puzzle of a big-league pitcher.

Pitch counts have received a lot of attention in recent years, as teams attempt to minimize the wear and tear on a pitcher's arm by limiting the number of throws that he makes in competition. A pitcher's workload also refers to the number of innings and/or pitches that he executes over the course of a season or career. Any assessment of injury risk is incomplete without knowledge of how a pitcher was handled throughout his amateur days. We hear about high school pitchers who are tasked with workloads that would make a professional coach cringe, and biomechanist Dr. Glenn Fleisig has hypothesized that the growing popularity of year-round baseball is inflating overall workloads while shrinking (or removing) the physical rest/recovery period of the offseason. Today's professional pitchers are not expected to last much longer than 100 pitches in a game, and the developmental program has shifted such that many of these players are being worked harder as amateurs than as pros.

What we know about Fernandez: The Marlins have been very careful with their wunderkind’s workload. He has exceeded 110 pitches in a game just once in his career, and this season he had cleared the century mark in just three of his eight outings. His 3985 Pitcher Abuse Points (PAP) ranks a modest 34th among pitchers this season, yet he has already accumulated more PAP than he did in all of 2013, a year in which he totaled just 1640 total PAP in 28 starts (ranked 145th).

While it is directly tied to workloads, fatigue deserves its own category, given that each pitcher handles it differently. Pedro Martinez was a shell of himself once he got past 100 pitches, but his contemporary, Randy Johnson, could toss 130 with hardly any dent in his effectiveness. This is why pure pitch counts and stats such as PAP (with non-differentiated baselines), which are powerful when applied to a population, break down on an individual level. Some pitchers will compromise their mechanics as they tire, often sacrificing pitch command in an effort to maintain velocity, while others will ease off the gas.

The specific mechanical alterations also vary from player to player, often having an impact on positioning, timing, stability, and/or power. The key for each organization is the ability to recognize fatigue within each of their pitchers and to understand the risks when one starts to lose it. The onset of fatigue can follow very different patterns for each pitcher, which supports the use of more dynamic pitch-count thresholds that are tailored to each arm’s fatigue conditions. In the not-so-distant future, teams could have access to in-game data that compares present performance to mechanical baselines, allowing for an objective indicator of fatigue and taking much of the guesswork out of the equation.

What we know about Fernandez: He rarely displayed obvious signs of fatigue. The careful workloads likely contributed to his consistency, both in-game and between outings, and on most days Fernandez was able to maintain velocity from the first pitch to his last. His ability to hold velocity was not quite as strong in early 2014 as it had been last season, and in his final start the velocity took a sudden nosedive after he hit the 50-pitch mark, at a time when he was visibly laboring to execute his pitches.

Perhaps the most reliable indicator of future injury is pitch velocity, as pitchers on the far right tail of the velo curve consistently incorporate the highest levels of kinetic energy. In a vacuum, the guys who can pump high-90s gas task their bodies with higher joint loads that push the limits of physical function. The hardest throwers are also the most sought-after, from the time that they are teenagers (trying to impress dads, coaches, and scouts) on up the minor-league ladder, which adds to the devastation when another young flamethrower goes under the knife.

There are also injury concerns tied to nearly every type of secondary pitch, with entire organizations disdaining the cutter or distrusting the splitter. Breaking pitches get the most publicity in this arena, as curveballs and sliders that require a large degree of pre-set supination can be tougher on the arm, given that the amount of pronation that takes place after release point is naturally greater. Supination is one method of throwing breakers, but the alternative is even more dangerous: a late twist of the wrist near release point that compounds the injury risk during the most intense phases of the delivery. Many coaches will limit breaking-ball frequency as part of their plan for workload management, since throwing 60 fastballs and 40 curves is more taxing than an 80/20 split.

What we know about Fernandez: He throws really, really hard. His average fastball velocity of 96.6 mph ranked as the fifth-highest mark in baseball this year (minimum 200 fastballs). His breaking ball is one of the nastiest pitches in the game, but he requires a great degree of supination in order to generate the ludicrous movement on the pitch, and his use of the Defector had grown to worrisome levels. Fernandez threw the pitch 33.8 percent of the time in 2013, and that rate rose to 37.2 percent this season. He began to utilize his changeup more often over his final three games, but he threw as many as 54 Defectors (out of 109 pitches) in a single game this season, and he has thrown the second-most curves in baseball in 2014.

Mechanical efficiency plays a big role in pitcher health and effectiveness, but it often becomes the scapegoat when a pitcher gets injured. I wrote an article two years ago (nearly to the day) that discussed the role of mechanics in the injury calculus, and though we have identified a couple of mechanical precursors amid a plethora of hypotheses, we lack evidence that has been substantiated through rigorous scientific testing.

The mechanical report cards that I put out for each pitcher are based on biomechanical efficiency and functional utility, but there exist some double-edged swords that effectively blur the line between function and safety. For example, efficient mechanics can help a pitcher throw harder, but the resulting increase of kinetic energy through the system elevates the overall risk of breakdown. To truly understand a pitcher's physical injury risk, we have to acknowledge the connecting links in the chain that have a direct influence on his mechanical efficiency and personal signature. Workloads, fatigue, conditioning, and genetics will all influence the delivery, and mechanical inconsistency has the potential to accelerate injury.

What we know about Fernandez: Fernandez has some of the best mechanics in the game. His report card is remarkable, with plus grades in every category and an overall score that is almost unfathomable for a pitcher his age. He has a blend of stability, power, and consistency that fuels his incredible stuff and stellar command. In 2014, the balance and posture had been slightly behind last year's peak, and he had altered his stride direction to finish a bit more closed off, but such trends are common early in the season, and the overall package was still one of the best in baseball.

Mechanics Report Card









Release Distance






For an explanation of the grading system for pitching mechanics, please consult this pair of articles.

There’s a wide array of theoretical approaches to preparing a pitcher for the physical task of throwing baseballs for a living, and behind every mechanical report card is a pitcher's workout regimen and training technique. Ideally, a pitcher will have the functional strength and flexibility necessary to support his delivery, but success in this area requires a balanced approach to conditioning that emphasizes the top half and lower half, front side and back side, in order to support all of the links in the kinetic chain. The needs of each athlete are different, and players won't react the same way to various approaches, so the training methods of each athlete are potentially all over the map. The conditioning aspect is perhaps the most underappreciated of the risk factors for injury.

What we know about Fernandez: He has a great reputation as a hard worker who is dedicated to his craft, but there is very little information available to the public that would help us properly assess his training methods. The Marlins have a much better idea of how Fernandez’s physical preparation is supporting his development.

A player's biology goes further than his listed height and weight, and there are many elements of a pitcher's DNA that are simply unknown. There is wide variation among the pitcher population with respect to muscular function and structural integrity of the joints, such that some pitchers can withstand stresses and joint loads that would break other hurlers. Jake Peavy is a perfect example: his delivery features heavy elbow drag that puts tremendous stress on his throwing arm, yet when his system snapped it was a back-side shoulder muscle (latissimus dorsi) that popped off of his humerus while his UCL remained intact. Peavy's detached lat, an unprecedented injury for a pitcher, also revealed something about his unique biology.

What we know about Fernandez: We know next to nothing about his genetics, beyond the visible evidence of a prototypical pitcher's build at 6'2” and 225 pounds.


It’s tempting to look for causation when we suffer a loss like that of Fernandez, and the UCL epidemic of 2014 has put injuries at center stage, but we need time to put some distance between logic and emotion in order to gain a reliable perspective. We could look back at this season as a blip on the radar, or it could turn out to be a turning point in the understanding of pitcher injuries, but the possibility of the latter scenario rests on the recognition of the former. Baseball will miss the exhilarating talent of Fernandez for the next 12-18 months, but rather than over-analyze his scenario in an attempt to find the smoking gun, we can take a step back and reconsider our approach to the mystery of injury prevention by appreciating the interconnected nature of the risk factors involved.

In the meantime, we still have 36 Fernandez starts in the MLB.TV archives to sustain us.

Thank you for reading

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WHAT? No mention at all of the fact he was puking his guts out right before gametime? And management still let him pitch? You forgot a category: Dehydration. Or maybe it should be called, Manager Stupidity.
Are you implying that his potential/possible dehydration lead to the UCL tear? That'd be a new one!
Check it:
Also Will Carroll said this:

Add in that Fernandez was ill before the game and potentially dehydrated, which can have a massive effect on the body, and no one comes off looking good.
Was this intentionally a demonstration of the point that "It's human nature to attempt to isolate a singular cause when something goes wrong, but science rarely affords us the convenience of simplicity..."?
I did indeed forget a category: Health.

This can be internal (ie dehydration) or external (ie the thigh bruise), and it is intertwined with each of the other six categories. These elements were not direct causes for Fern's injury - according to Dr.'s Andrews and Fleisig, UCL's wear down over time rather than pop in a single day - but they may have elevated his risk in that particular outing. Health is also a category for which we have very limited information, and players can be very different with how they respond when health is compromised.

We are also not in a position to assign blame for this injury, and it's too bad that the lawyer's statement have added fuel to the fire.

Also see comments in this thread. Some good stuff there.
Scientists know only too well that when things go wrong, it is almost always the case that multiple factors are involved. Loss of mechanics resulting from his "flu-like symptoms", which others have suggested to be the cause, may have contributed. Do we have any evidence that Fernandez lost his mechanics, something like a change in arm slot or release point, that occurred during this last start before the velocity drop-off?
There was an excellent roundtable discussion on the MLB network just under a week ago. I finally got around to watching it yesterday. Bob Costas Moderated and other panelists included Jim Kaat, John Smoltz, Tom Verducci. It was a very thoughtful, insightful serious back and fourth debate on the issue and highly worth watching. It was a refreshing change from the kind of silliness that passes as discourse on the four letter network these days.
Why is everyone looking to blame someone for this injury? It's like when the SF fans starting crying when Buster went down. Maybe we should start having pitchers throw underhand, because the strain on the elbow is significantly reduced that way. The fact is his UCL couldn't take the power and torque that was being put on it with the way he threw and it got shredded. Stop with the witch-hunting Captain Hindsight. I mean, just read the front cover of BP this year. It seemed like they were expecting an injury from Jose prior to the start of the season, as usual, they were right.
MLB needs to address this with a new rule. New rules are the answer to everything! If not a new rule, then I bet we can fix this with replay.
Why does the fact that kids are beginning to throw breaking pitches at younger and younger ages never factor into this discussion? I do private instruction for a living and I see kids as young as 9 and 10 already throwing a high amount of curveballs and sliders in games. This is an age when arms are developing the most and this must be doing a ton of damage to their arms. To me it's no coincidence that this rise in the level of UCL injuries is happening along with this growing trend. When I was a young ball player, my father and coaches wouldn't even show me the grip for a curveball until i was in middle school. But now there is so much pressure put on these kids by their parents and their coaches in these highly competitive leagues and there seems to be no regard for how they should be properly developed. I think we are now seeing the product of this mentality. I am not a doctor though, so I would like to see this issue addressed by a medical professional.
The simple answer is that IT WAS NOT A SINGLE EVENT which led to the injury. He is too young to be attempting to do what he was doing. This happened last season when he was promoted #unsustainable.