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Here’s how the Brewers pitching staff looks when ranked by Average Runs Prevented. For additional context, each pitcher’s Games, Games Started, and Innings Pitched statistics are included.

Stats: 

Average Runs Prevented is the average of park-adjusted, league-adjusted estimates of a pitcher’s actual runs allowed compared to their expected runs allowed.

DRA Runs Prevented is the difference between a pitcher’s expected runs allowed and their DRA performance. 

Direction is the “Direction of Change” between a pitcher’s 2018 Average Runs Prevented and 2018 DRA Runs Prevented.

G is “Games” (total appearances); GS is “Games Started” (total starts); IP is “Innings Pitched.”

Why is this important? DRA is a pitching statistic that estimates each pitcher’s performance based on numerous contextual factors. DRA is a statistic that can describe a player’s performance on the field by correlating Runs Allowed per 9 IP (RA9) to DRA; it is modeled to consistently assess a player’s performance year-to-year; and it is modeled to predict next year’s RA9. Runs Prevented, on the other hand, is a purely descriptive statistic, simply aiming to measure the extent to which a pitcher compares to their park and league environments.

Before we get into the extended analysis, if you’d like to know why this topic is important, consider the following questions; for fun, the exercise could also end here, as there’s a lot to think about with this staff.

….which of these pitchers would you expect to improve in 2019?

….which of these pitchers would you expect to improve in 2019?

….which of these pitchers would you expect to improve in 2019?

By describing Runs Prevented and DRA Runs Prevented statistics year-over-year, it is possible to understand the absolute volatility of pitching performance. DRA is also potentially a tool that can be used to set someone in the right direction for analyzing statistical profiles in order to project improvement or decline.

Let’s take a look at MLB pitchers that worked in 2017 and 2018:

The value of using a statistic such as DRA is that the year-to-year Runs Prevented performance by MLB pitchers is absurdly volatile. The table above demonstrates the absolute value of change in several key statistics for pitchers that worked in both 2017 and 2018. 639 MLB pitchers worked in both 2017 and 2018 seasons. On the whole, this group was quite volatile, with the average change in runs prevented moving by nine runs prevented (positive or negative); a pitcher that worked in both 2017 and 2018 also saw their innings pitched total fluctuate between 33 and 34 innings, and their average games started fluctuate by four. Focusing specifically on starters (i.e., pitchers who started a game in 2017 and pitchers who started a game in 2018), the fluctuations are even wider.

These fluctuations would be the equivalent of Jhoulys Chacin becoming a slightly below average, slightly smaller workload pitcher in 2018, or improving steadily into “ace” territory; Freddy Peralta expanding into a more regular rotation role, or stepping back into a smaller replacement role; Corey Knebel fluctuating to a below average reliever or recovering his excellent high leverage form; or Josh Hader becoming “just” an average reliever or taking the next step in his high leverage ace development. These are just a few examples of the real impact that typical run prevention fluctuations can cause to a team. Each of these pitchers are likely to remain under Brewers contractual control in 2019, so it matters how their performances change.

Let’s dig deeper into that group of 639 pitchers that worked in both 2017 and 2018 to assess the descriptive value of DRA and Runs Prevented. A couple of caveats are in order. First, this is a biased analysis, insofar as I am expressly limiting my search to players that worked in both 2017 and 2018, which excludes a “true talent assessment” of players that missed either of those seasons for a multitude of reasons (from player development, such as Freddy Peralta, to injury, such as Jimmy Nelson). Second, since I will be describing the general direction of DRA, I am not using statistical methods to assess the significance of DRA’s predictions. With these caveats in mind, I think it remains useful to see how DRA assesses players within a single season, and across two seasons.

Now that we’ve discussed the average absolute value of Runs Prevented change between 2017 and 2018, let’s take an overview of this group of pitchers in terms of improvement or decline. Excluding pitchers with Runs Prevented totals between -2 and 2 in 2017 and 2018, which represents a relatively minimal range of fluctuation that could simply be explained by park factors or league environment, more pitchers declined than improved between 2017 and 2018. In many cases, these changes were quite major, as 132 pitchers declined by 10 or more Runs Prevented, while 53 pitchers improved by 10 or more Runs Prevented. The overall magnitude of major declining performances ensured that this group of 639 pitchers was -439 Runs Prevented (!!!) between 2017 or 2018; this means that if each 2017 team retained these pitchers, on average they would have been expected to lose approximately 44 more games (as a group) in 2018, all else held equal.

Based on 2017 performance, could anyone have predicted these directions of change among these pitchers? Once I assembled an Average Runs Prevented analysis of the 2017 MLB season, and isolated pitchers that worked in both 2017 and 2018, I analyzed several aspects of each player’s performance:

• I analyzed the 2017 Direction of Change, which is the change between 2017 Runs Prevented and 2017 DRA Runs Prevented, in order to assess whether a player overperformed or underperformed their DRA.

• I analyzed the 2017 Direction of Change and the difference between 2018 Runs Prevented and 2017 Runs Prevented, in order to assess whether a player’s between-seasons change (2017 to 2018) matched their 2017 underperformance or overperformance. Focusing on 2017 Direction of Change and between-seasons change is one way to describe the types of projections made by DRA.

• I assessed 2017 DRA Runs Prevented and 2018 DRA Runs Prevented in order to determine whether the statistic consistently estimated a pitcher’s contextual performance.

First and foremost, in terms of 2017 and 2018 consistency, DRA consistently assessed 389 pitchers as either Above Average or Below Average in both 2017 and 2018. Since the “Other Pitchers” group is quite a set of outliers, I provided a couple of key statistics about their DRA Runs Prevented.

In this case, the “Other” group is comprised of outliers, including pitchers like Wade Miley and Chase Anderson, as well as Lucas Giolito, Kyle Freeland, and Derek Holland, among others. This is an area where the biased selection of this group of pitchers could impact analysis, as developments such as a new pitch (by Miley) or backed-up stuff and command (by Giolito) create role discrepancies that would be difficult to predict without granular scouting information. Of course, these are precisely the types of uneven player development facts that teams attempt to exploit. Wade Miley was not a particularly good pitcher in 2018, indeed he could have reasonably been replaced (which is partially why he was available for a minor league contract entering 2018); his development to an average pitcher was worth 44 DRA Runs Prevented between 2017 and 2018, a massive improvement that is going to skew nearly any sample of players.

On the whole, it is worth noting that DRA Runs Prevented tracked better than Average Runs Prevented, in terms of absolute value of change, between 2017 and 2018. Among pitchers that worked in both seasons, DRA Runs Prevented fluctuated by approximately 8 runs, compared to approximately 9 runs by Average Runs Prevented. Not bad!

How does DRA work with this group of pitchers in terms of predicting the general direction of change between 2017 and 2018? Based on a pitcher’s internal 2017 difference between DRA and Runs Prevented, that pitcher’s typical improvement or decline between 2017 or 2018 matched the overperformance or underperformance (in terms of 2017 DRA versus 2017 Runs Prevented). DRA correctly assessed a pitcher’s expected performance change in 79 percent of cases:

Within this group of pitchers, DRA performs quite well in terms of assessing the actual size of the Runs Prevented change, as well as the direction. Once I categorized pitchers into groups of players that had Predicted Improvement, Predicted Decline, or some Other Prediction, I compared the change between 2017 and 2018 DRA Runs Prevented to 2017 and 2018 Actual Runs Prevented:

It should be underscored that this is a descriptive account of DRA’s predictions, rather that a statistical test of the significance of DRA’s predictions. Still, what is incredibly impressive about DRA is just how strong the statistic is in anticipating the shape of the run environment, and understanding the wide variance that can occur year over year.

What is interesting is that, according to DRA, the Brewers pitching staff was indeed better than average in 2018. However, there are 22 pitchers from that staff that might reasonably be expected to post a notable improvement or decline in 2019, if one assesses the extent to which they outperformed or underperformed their 2018 DRA. Thus, it is worth repeating the questions about who might be expected to improve in 2019, for even if the overall direction of the club’s pitchers may be expected to stay the course, their shape and distribution of Runs Prevented can all but expected to look quite different.

Junior Guerra has had an up-and-down season, which will deserve more analytical scrutiny once the season closes. Brewers fans largely wrote off Guerra after the righty experienced a forearm injury in July (on DL July 14-24), which preceded a truly dreadful stretch of baseball. Returning from the disabled list, Guerra started eight games, ultimately working 37.3 innings while allowing 38 runs (!!!) and a 32 strike out / 16 walk / 8 homer / 1.08 Groundball:Flyball peripheral performance. At this point, the Brewers replaced Guerra in the rotation with newly acquired southpaw Gio Gonzalez, himself looking for some redemption in a new locale.

Guerra’s fall was shocking in part because the righty maintained solid Runs Prevented throughout the year. On May 31, the splitter pitcher averaged approximately Nine Runs Prevented; that swelled to approximately 11 Runs Prevented through July, before returning to approximately Nine Runs Prevented on August 12 and plummeting to -1.3 Runs Prevented by August 24. Guerra bottomed out at an average of -9.0 Runs Prevented on September 9, meaning that the righty boasts one of the Top 10 Runs Prevented “declines” during the 2018 season:

What is notable, however, is that despite Guerra’s large decline from May through September, the righty ultimately provided (approximately) average production throughout the season. Ironically, Gio Gonzalez matches this trend for Guerra as well, as the lefty averaged approximately Four Runs Prevented for the Nationals despite falling to below average production by the time he was traded to Milwaukee.

So, the Brewers entered a playoff stretch run by moving one formerly productive starting pitcher into the rotation at the expense of another formerly productive starting pitcher. Yet, Craig Counsell provided Guerra a couple of opportunities to define his relief role while working in close deficits on September 11 and September 15, and the righty also made another appearance during last night’s series closing victory against the Reds.

I’ve dreamed on a Guerra relief role since the beginning, considering the righty’s command stature and splitter as two of the reasons that the righty might morph from a starting pitcher into a reliever. What is fascinating, however, is that while Guerra is absolutely lights out over 3.7 relief innings thus far (5 K / 0 BB / 0 HR / 1.33 GB:FB), that formerly elite splitter is nowhere to be seen. In fact, according to Brooks Baseball, entering Wednesday night’s match-up against the Reds, the righty had almost exclusively worked fastball / breaking ball in relief. At the time of this writing, Brooks Baseball data had yet to reflect Guerra’s last outing, but raw Gameday Play-By-Play suggests that Guerra was once more a two-pitch pitcher.

What is especially stunning about Guerra moving to a fastball / breaking ball relief profile is that the hurler is not even using his slider. According to Brooks Baseball, Guerra’s velocity, vertical movement, and horizontal movement profile on his breaking ball matches his previous “curveball,” rather than his well-known “slider.” Here’s how Guerra’s pitch profile looked as a starting pitcher in 2018:

To emphasize just how different this new version of Guerra looks from the old Guerra, here’s how Brooks Baseball classified his relief work in September 2017:

While it is too early to make note of any velocity changes on the fastball based on standard deviation on Guerra’s September fastballs as a starter and a reliever, it is worth diving into the sharp arsenal change exhibited by Guerra. According to Brooks Baseball, Guerra’s fastball / breaking ball blend is producing more whiffs and groundballs on his fastball than his starting pitching usage of the pitch, while the “curveball” effectively is acting like a splitter in terms of whiffs and groundballs. Notably, this combination of pitches finds Guerra working in entirely new areas of the strike zone with his fastball compared to his previous usage, with the caveat that this is an extremely small number of pitches to draw any meaningful conclusions.

With this curveball offering, however, Guerra has already thrown nearly as many pitches as a reliever compared to his entire time as a starter in 2018, and here it is worth noting that Guerra is scattering the pitch more evenly across the bottom of the strike zone while also moving it away from the upper-armside (inside against a righty bat) area of the zone:

Ultimately, I do not think assessing Guerra’s arsenal shift as a reliever is “much ado about nothing,” as the righty is suddenly answering a crucial question entering potential playoff series: who can help to stretch out close deficits? Granted, in the playoffs, pitchers like Jeremy Jeffress and Josh Hader will probably experience higher workloads. However, since the Brewers seemingly base Hader’s workload off of his recovery time, adding another reliever that can effectively work a couple of frames is extremely important (especially as starting pitchers work shorter outings as the season winds down). It cannot be understated that Guerra is also working for his future with Milwaukee, a club that is also arguably designing an unorthodox pitching staff that is based around systemic runs prevention rather than standard 1-through-5 starting pitching assessments. This is undoubtedly one reason Guerra had a job to begin with, and undoubtedly one reason the Brewers gave the righty every chance to succeed as a starter. Guerra the reliever could still potentially fit into a 2019 pitching staff that may double down on amorphous roles after general 2018 Runs Prevented success.

Now, perhaps it is time to dream bigger on that relief role for the stretch run, potentially the playoffs, and for 2019; in this regard, it is also time to scrutinize a relief role for Guerra. If it can be stated that Guerra exhausted the utility of his fastball / splitter / slider arsenal in Milwaukee, a new look at a hard, rising fastball and slightly slower curve combination could find the age-33 hurler staying on for at least one more go ’round. In this regard, it’s interesting to think about the pitchers in Milwaukee that have benefited from learning Guerra’s splitter, and now view the righty as a beneficiary of Pitching Coach Derek Johnson’s curveball instruction (recall that this is the pitch that revitalized Jimmy Nelson and Chase Anderson). When one role ends for a pitcher, a new pitch can present a new role; while this should not be viewed as magical thinking, nor a fail-proof development, for now it should be viewed as a new opportunity for Guerra to bolster Milwaukee’s high leverage relief group.