Despite the fact I used the phrase in the title, I don't like the term "sophomore slump." Sure, it's alliterative and rolls off the tongue nicely, but it's too simple. When I hear "sophomore slump," I think random variation getting a guy down. Maybe I'm focusing too much on the "slump" part. What people really refer to when they say the phrase is the phenomenon that rookies who burst onto the scene often struggle in their second year. Jedd Gyorko was such a player.
After accomplishing the whole bursting onto the scene thing as a rookie by hitting 23 home runs in 125 games in 2013, Gyorko followed by being generally terrible in 2014. All the results were worse, but the process was not necessarily broken. Gyorko actually increased his walk rate and decreased his strikeout rate. Unfortunately, a decrease in strength of contact resulted in Gyorko's production being far less than stellar. At the beginning of June, Gyorko was slashing only .162/.213/.270 when the Padres placed him on the DL for plantar fasciitis. Gyorko was on the 15 day DL until late July which, for those who are counting, was far more than 15 days.
Former Beyond the Box Score writer Stuart Wallace penned a fantastic piece on what effects plantar fasciitis had on Gyorko. As you might expect, the basic idea was that all aspects of baseballing were affected by the injury. I recommend you read the article since Stuart explained it so well, but PF affected Gyorko's swing in multiple ways, which was a likely cause of Gyorko's poor performance.
Because of the timing of his injury, Gyorko's first half split represents time during which he could have been playing injured. His second half split represents time during which he could have been playing healed. The difference is stark.
When combined with the timing and knowledge of the plantar fasciitis injury, the difference is so large that I find it difficult to accept random variation as the only cause. Occam's razor, right? While on the DL, Gyorko said he spent some time soul-searching (staring at his stats probably wasn't fun) and watching video of his at bats. He apparently found some differences between his 2013 and 2014 at bats. Perhaps whatever he changed helped. Here are his batted ball rates comparing the two "halves."
It looks like Gyorko was able to make much more solid contact after returning from injury. There's some fire behind this smoke.
In addition, Gyorko noted that pitchers were pitching him differently, saying that he was chasing off speed stuff outside more than he should have. He said that word got around.
As 2013 wore on, pitchers threw him more junk to try to avoid his power. However, pitchers slowly increased their fastball percentage to him in early 2014. Perhaps word got around very quickly that Gyorko couldn't do much with any pitch, and it was only later that the injury finally became too much. Here are zone maps comparing 2013 to 2014 showing where pitchers located their offspeed stuff against him.
It does seem a bit like pitchers tried to keep their offspeed stuff out of the zone in 2014 compared to 2013. As far as his swing rates against offspeed stuff out of the zone, I don't think there's much of a difference. Too small a sample size. Gyorko actually swung less in general in 2014 compared to 2013, so that's what shows up, if anything.
Gyorko's 2nd year in the league didn't go very well. Some might blame that on the sophomore slump curse, phenomenon, or whatever you want to call it. I'd blame it on plantar fasciitis.
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