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The Effects of Tommy John Surgery on Batters

The new prevailing trend in major league baseball is a disturbing one. It is a trend of exponentially more frequent Tommy John surgeries. During the surgery, the ulnar collateral ligament is replaced by a different tendon from elsewhere in the body. As would be predicted, pitchers suffer from the injury much more than batters because they are constantly stretching their arm to full extension and pitching at high velocities. However, there are times when batters must have their UCL repaired. The unfortunate truth is that there is little data on what may happen to batters when they return. Most analysts report that the surgery has little to no effect on batters’ performance. This isn’t true.

My search for answers began when I heard the news that Matt Wieters, the Baltimore Orioles catcher, would need to undergo Tommy John surgery. Suddenly, I realized that nobody really knows how he will fare when he returns next season. Same thing applies to Minnesota Twins’ top prospect Miguel Sano. Sano, the Twins’ powerful third baseman of the future, had to have his UCL replaced before the season began to the disappointment of prospect and Twins fans alike. The same kind of disappointment felt when Jose Fernandez needed to have Tommy John surgery. The injury is affecting more players at an exponential rate and there is little data (particularly in regards to batters) that suggests how it will affect them when they return.

I scoured the internet for the complete list of players who have undergone the procedure and came across a massive list of 737 confirmed players (major and minor leagues) and crossed out everyone that was not a position player. I was left with a meager list of 29 names from the major leagues (minor league players were excluded because of the distinct differences from each minor league level). After removing even more names of players who may have appeared briefly in the major leagues or had the surgery and never returned to playing, I was left with just 15 confirmed names. Stars of the times like Paul Molitor, one of the very first recipients of the surgery, and lesser known players like Kyle Blanks both stood out on the list.

The next step in the process of unraveling the mystery behind the surgery was to figure out how the surgery affects the batters. In other words, I wanted to test if different tools were affected and in what ways. Did batters hit for the same amount of power as they did before? To begin, I collected data to test for three different measures of arm strength. Batting Average on Balls in Play (BABIP) determines the rate at which balls put into play are turned into hits. While this is not entirely based on arm strength, arm strength is a large factor in placement of the ball coming off the bat. A more powerful swing will lead to more balls in play being turned into hits. More on that here. Slugging percentage (SLG) was the next piece of data I tested for. If a batter could hit the ball further, then they could have more extra-base hits. Similarly, I tested for Home Run to Fly Ball percentage (HR/FB). This measures the rate at which fly balls go over the outfield walls and become home runs. Another barrier to success, as can be seen in the image below, was that there was no recorded advanced fielding data prior to 2002. So it is possible that the HR/FB data is less diluted by sample size than the other measures.

TJ Batter Data

Honestly, the results were surprising. Like most analysts, I believed that they would be right in saying that the surgery has little to no effect on batter strength. I found this to be wrong though because, on average, most batters did experience a non-negligible decrease in BABIP, SLG, and HR/FB.

TJ Batter

Of the 15 tested batters, 12 experienced a decrease in BABIP, culminating to an average decrease of 0.015. In the sabermetrics world, statistics dictate all research and this is no exception. A 0.015 decrease is another way to say, “1.5% less balls in play lead to hits”. Whether this can be attributed to luck, fielding, or less power is another question. But with over 65,000 at bats worth of data, there should be a sizable amount of batter-driven results rather than deferring the results to worse luck or better fielding. In perspective, a 1.5% decrease in batting average causes a drop from .300 to .285.

Slugging percentage was the most impactful finding though because, of the 15 batters, 11 experienced a decrease in slugging percentage. A reminder that each surgery occurred at different points in the batters’ careers, meaning that natural weakening with age should be filtered out. Overall, the data combined to form a 0.419 drop in slugging percentage or an average 0.028 decrease post-Tommy John surgery. 2.8% less hits were extra-base hits for the remainder of these batters’ careers. A significant amount when considering that some of these batters had careers lasting fifteen years or more. Home Run to Fly Ball rate had to be adjusted to take into account the emergence of fly ball data in 2002 (I removed the home runs hit before 2002 before calculating). Of the 9 batters tested, now 7 of them experienced a decrease in their HR/FB rates. This all comes out to be a 0.018 decrease, meaning 1.8% less fly balls zoomed out of the park and into the stands. The major league average usually stands at 10% but these batters saw their power drop from 10.1% to 8.3% after the surgery.

The only thing left to say is that analysts and fans alike need to recognize the fact that Tommy John surgery does have a negative effect on a batters’ power. Mostly though, I’m disappointed Miguel Sano’s power will never be what it could have been.

Thanks to FanGraphs for all batting and advanced fielding data and for the complete Tommy John surgery encyclopedia

Analyzing Yoenis Cespedes

Yoenis Cespedes struggled at the plate this year for reasons unknown to most. Analyzing why he struggled in 2013 versus why he was deemed excellent in 2012 all comes down to sabermetrics. Cespedes’ biggest enemy was actually… himself. Through research and statistics, Cespedes swings at too many inside pitches in an attempt to hit more home runs. The pressure from his overshadowed rookie season may have come back to haunt him this past year. His batting average dropped from .292 to .240 and his OPS fell from .861 to .737 all because of a few changes Cespedes made at the plate. The statistics easily point out the causes for Cespedes’ struggles and how he might be able to fix them for next season. Even though it may seem that Cespedes was a much worse batter in 2013, that is not the entire case. He actually was much better at making contact with pitches thrown to the outside of the strike zone, boasting an increase from 59.5 % to 63.7 %.

   1.  Swinging at Inside Pitches Too Often & Taking Too Many Strikes
Cespedes took a swing at way too many pitches inside the strike zone this season. A number that increased from 65.3 % to 71.8 % from 2012 to 2013. In comparison, when Adrian Beltre took a swing at 71.6 % of inside pitches in 2005, he hit .255 with just a .716 OPS. In addition, when swinging at such a high amount of inside pitches, Cespedes’ hit a lower percentage of them as well — going from 84.0 % in 2012 to 80.4 % in 2013. As a result of his tendency to swing more often at inside pitches, he saw an increase of strikes by 2.5 % (1233 of 1979 in 2012 to 1407 of 2169 in 2013). More strikes lead to more strikeouts and a lower batting average. His strikeout rate increased from 18.9 % to 23.9 % just over the course of a single season.

Swinging at the amount of inside pitches that he did, power pitchers took full advantage of his swing, resulting in a .196 batting average. Against finesse pitchers, Cespedes averaged a .263 batting average. (power pitchers are defined as the top third of pitchers when combining the amount of strikeouts and walks. finesse pitchers are defined as the bottom third) When Cespedes fell behind in the count, he proved to be an easy out; with two strikes and any amount of balls, he batted a horrifying .130. Also, Cespedes is often too eager to swing at the first pitch of a plate appearance when he does not have a trace on the pitcher’s style or location. Swinging at the first pitch resulted in a .209 batting average whilst taking the first pitch resulted in a .252 batting average.


2.  Pulling Too Hard for Home Runs
Cespedes certainly tried to hit as many home runs as possible this season; he did pass the previous year’s number of 23 by three and his power assuredly grew. As evidenced by his spectacle at the home run derby, Cespedes possesses a strength like few others in the MLB. However, he often tried too hard to get the ball over the wall, resulting in an increase in fly ball rate from 39.9 % in 2012 to 45.6 % in 2013. The pressure to improve from critics and fans alike might have pushed Cespedes into trying to hit more home runs than he possibly could. Given his time on the DL due to nagging hand injuries, it surprised most that he even hit this many home runs — either because of lost time or wrist pain.


                                                             The power is definitely still there

 3.  BABIP (Batting Average on Balls In Play)
Cespedes was also just plain unlucky in 2013. BABIP measures the percent of batted balls that end up as hits — either because of defense, luck, or positioning. Basically two-thirds uncontrollable to the batter and one-third placement of the bat. Cespedes ended the 2013 season with a .274 BABIP; whereas the standard and league average nowadays hovers around .300. In 2012, he finished with a .326 BABIP — a lot luckier than this past year. The second reason (pulling for home runs) most likely factors a moderate amount into the regression too. Unfortunately, the causes of BABIP can disguise a player’s true skill level behind solid defense, timing, and bad luck.

The real Yoenis Cespedes is most likely somewhere in between his two major-league seasons but much closer to his rookie season than 2013. Yoenis Cespedes thrived in the spotlight but collapsed under pressure in 2013. His statistics in the 2013 playoffs alone describe his love of the spotlight (.381/.409/.667). Not only does he play well in the playoffs, but he also crushed everyone else in the home run derby this year. Expect Cespedes to be a big bounce-back candidate in 2014 after he can look at why he struggled at the plate. Upon arriving in America from Cuba as a free agent, Cespedes was hailed as a five-tool player and “arguably the best all-around player to come out of Cuba in a generation.” Don’t give up hope on the Athletics’ outfielder just yet.

For more articles like this, visit my baseball analysis and news website: The Wild Pitch

All statistics courtesy of baseball-reference and FanGraphs: