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What does past quality of opposition tell us about the Rockies' 2015 rotation?

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Mark J. Rebilas-USA TODAY Sports

Several times a week, I learn something new about baseball by reading articles about baseball. It’s usually not something as simple as discovering the existence of a thing. But that happened when I read a piece by Jeff Sullivan at FanGraphs earlier in the week. In it, he investigated James Shields’s quality of competition based on a statistic from Baseball Prospectus, oppRPA+. This metric approximates and works the same way as an opposition’s wRC+ (100 is league average). I didn’t know oppRPA+ existed, but its existence makes sense. How good was a given pitcher’s opposition over the course of a given year? That is a question worth pursuing. It deserves attention even though, as Sullivan points out, the answer to the natural follow up question—what does the quality of opposition tell us about a pitcher’s talent and chance to succeed in the future?—is frequently "not much." But what it does do is help contextualize individual pitcher seasons.

In general, the weakest competition a pitcher will face is an oppRPA+ of 95 or below, but not too far below. On the other extreme, an oppRPA+ of 105 or over signals the strongest competition. The range is not that big; pitchers simply face too many batters over the course of a season for the quality to be either extremely poor or extremely good.

To add some helpful context to Rockies pitcher seasons from the recent past, I identified the season-by-season oppRPA+ for the careers of the expected 2015 Opening Day starting rotation. To wit (injury shortened seasons italicized):

oppRPA+, 2007-2014
Jorge De La Rosa Jhoulys Chacin Tyler Matzek Kyle Kendrick Jordan Lyles
2007 102 -- -- 97 --
2008 99 -- -- 100 --
2009 100 -- -- 102 --
2010 103 103 -- 104 --
2011 95 96 -- 98 99
2012 98 98 -- 99 99
2013 91 94 -- 92 107
2014 95 97 98 97 95

The nominal ace of the Rockies’ staff, Jorge De La Rosa, only had one outlier season. In 2013, he faced batters who collectively hit nine percent below league average that year. Unsurprisingly, this was De La Rosa’s best (full) season in terms of ERA (3.49) and FIP (3.76). Those figures are among the best single season marks in team history. It’s also worth noting that his home run to fly ball ratio that season was a very low 7.7 percent. Improved quality of opposition in 2014 resulted in increases in De La Rosa’s ERA (4.10) and FIP (4.34). His HR/FB rate also increased to 12.9 percent.

Jhoulys Chacin’s best season also came against his weakest competition. His ERA and FIP mirrored each other at 3.47. Like De La Rosa, the most noticeable way Chacin exploited the competition was by limiting home runs. His HR/FB ratio that season was 6.2 percent. We’ll have a chance to see how Chacin adjusts to what will almost certainly be higher quality bats in 2015. We didn’t get this opportunity in 2014 due to Chacin’s shoulder issues.

Tyler Matzek’s roughly league average competition during his rookie season only tells us that, on the whole, he wasn’t helped by weak competition and didn’t excel against strong opponents.

New Rockie Kyle Kendrick’s season-to-season opponents have hovered around league average, with the exception of 2013. Interestingly, 2013 was not Kendrick’s best season in terms of ERA. He finished the season with a 4.70 ERA. His 4.01 FIP, however, is the best mark of his career thus far. Against the weakest single season competition, Kendrick also was able to keep the ball in the park. He had a 9.5 percent HR/FB ratio, which was the best of his career.

Jordan Lyles presents an interesting case because he had a dramatic swing. In 2013, the bats Lyles faced collectively hit seven percent better than league average. The result was an awful 5.59 ERA for the Houston Astros. In 2014 for the Rockies, he faced batters who collectively hit five percent below league average—a twelve percent difference from the year before. Lyles, of course, had a much better season, as his ERA fell to 4.33. Most interestingly, and possibly most worryingly, his home run to fly ball ratio was the about the same in both years: 11.6 percent in 2013 and 11.9 percent in 2014. In other words, the correlation between below average quality of opposition and low HR/FB ratio that appears for the other pitchers did not do so for Lyles in 2014. Part of that might be due to Coors Field, but in 2014 Lyles gave up as many homers on the road, six, as he did at home.

Two other 2014 tidbits: We knew that Eddie Butler faced tough competition in 2014 because he faced the Dodgers for two of his three starts, but to put a number on it the batters he faced were seven percent better than league average. Adam Ottavino also faced an oppRPA+ of 107, which makes his season out of the bullpen all the more impressive.

Saying that a pitcher’s best season came against the weakest competition isn’t a slight. Good pitchers should do well against weak competition, just like good teams should regularly beat bad teams. And pointing out that a pitcher’s weakest season came against above average competition is just an acknowledgment of the luck of the draw. In that respect, we gain a touch more explanation about good and bad seasons.

The anomalies are where we learn things. It is there where we affirm that Adam Ottavino can be a relief ace—and it’s where we wonder how long Jordan Lyles can stay in the rotation.