The Mariners signed Kyle Seager to a fairly large extension earlier this offseason. I'm not here to talk about that. Jeff Wiser covers it here. I am here to talk about a certain specific element of Seager's performance.
Seager has had a fairly steady rise in offensive performance that is expected from what we know about aging curves. Seager's wRC+ has increased from 96 to 108 to 115 to 126 during his time in the majors. His most recent season included a slight power outburst that saw career highs in ISO and HR/FB. It is this power burst that might be the small reason to worry about Seager.
I would like to point out that Seager was only 26 years old for the duration of the 2014 season. It makes perfect sense given his age that a power breakout would occur. This should be kept in mind going forward.
I find the power breakout a bit suspicious. I'll present various data points that led me to this conclusion. First, his ISO numbers. He did have a large increase from 2011 to 2012, but 2011 was only a partial season, and his rookie season at that. There was no significant ISO increase from 2012 to 2013. The wRC+ increase was driven by an increased walk rate; in fact, his BA and SLG numbers were almost unchanged from 2012 to 2013. This same line of thinking applies to his HR/FB rate, which increased in 2014 but not from 2012 to 2013.
The next piece of evidence lies in his production numbers by batted ball type. Given his home environment of Safeco Field, I would expect Seager's production on fly balls to be depressed. It's difficult to produce on fly balls in that stadium. Witness Seager's fly ball production on a yearly basis (Rel PRD is calculated by (1.7*BA+SLG)/(1.7*lgBA+lgSLG)*100):
|FB Rel PRD
There was a very large increase in 2014. Seager's fly balls showed a large increase in both ISO and BABIP. Again, since he was only 26, it's not out of the ordinary. However, the third piece of evidence might be able to strip just a little bit more context from his production to get at the process. Here are Seager's average yearly fly ball distances from Baseball Heat Maps:
|Avg FB Dist
Seager's average fly ball distance fell from 2013 to 2014, yet his BABIP, HR/FB, and overall production increased. This suggests to me that Seager's 2014 performance could be a spike preparing to regress.
So that's why I am slightly worried about Seager going forward. Because of his home park, his power will probably always be a bit depressed. It wasn't very depressed in 2014. Notice, though, my qualifying words. Small reason. Slightly worried. I'd like to point out a trend that occurred in 2014. Could be nothing. Could be something.
Seager's performance dropped pretty hard after the All-Star break. Seager's BABIP, ISO, and wRC+ all dropped significant in the "2nd half" compared to the "1st half".
Most of that decline showed itself in August and September. I'd like to combine this data point with the trend line of his batted ball distance through the 2014 season. The following image is from Baseball Heat Maps.
There was a corresponding decrease in fly ball distance during roughly the same time period as Seager's overall decline in performance that held down his 2014 overall numbers. Though Seager logged no time on the disabled list, I suspect injury may have been at play here. According to this article by former-Royals-now-Mariners beat writer Bob Dutton, Seager experienced a similar decline near the end of 2013. Seager refused to attribute it to "fatigue" or "fading". He attributed the 2013 decline to being in a "bad (hitting) position". Seager said that he now knows what to do should he find himself in a bad way, and it's possible that it made a difference. Seager's late-season decline in 2014 was far less than 2013.
It's possible that Seager's mechanics wear down through the course of the season, and he struggles to correct them later in the season. It's possible that the little aches and pains add up over the season. Nevertheless, Seager performed at a high level in 2014 compared to other years; because of the evidence presented above, I expect those numbers to regress. It's also possible that Seager has found ways to help him maintain a higher level of performance throughout the season. Combined with his mythical age 27 season in the upcoming 2015 year, Seager may not decline much at all. See? Small reason.
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Kevin Ruprecht is an Editor of Beyond the Box Score. He also writes at Royals Review. You can follow him on Twitter at @KevinRuprecht.