Fluctuation Race

The 2017 Cubs had a good rotation, as far as typical, standard rotations go. The club entered the season with their four most productive starters locked in, and many pundits praised their depth moves to fill out the back of the rotation. When a team can prevent more than 100 runs on the front end, and really offer at least three comparable arms in terms of quality, heading into the season with question marks or gambles on the back end is not necessarily a problem. While there were fans and analysts that questioned the Cubs’ roster building approach in terms of pitching, those claims were also hotly debated and rejected with seemingly sound logic: if the Cubs had pitching depth problems, everyone had pitching depth problems, and anyway the Cubs’ problems weren’t as bad as the others.

Except the pitching would indeed prove to be a problem for the Cubs, one that fully defined the club’s descent from “great team bordering on dynasty” to “just another very good team.” The distinction is crucial, for the Cubs slip left the door wide open for an upstart Brewers club that chased their big market foes deep into September; the two clubs played an extremely close series in Milwaukee in September that allowed the Cubs to finish the Brewers’ divisional aspirations, but the Brewers pushed the Cubs as hard as they could. The Cubs rotation would nearly be shambolic compared to its 2016 version, if fans were to forget that 14 runs prevented from the first four starters in a rotation is quite solid.

On the other hand, the Brewers entered the season with a rotation full of question marks. Ace Guerra would be returning for his second career season, after taking the world by storm as an age-31 rookie in 2016. He could not make it through his first start before the Brewers needed their first depth option. Wily Peralta came on strong to close the 2016 season, but quickly showed that those results were a mirage. That the front office kept Matt Garza around could lead one to question just how “analytical” this club is, as the righty’s first three years in Milwaukee proved his release at $12 million+ would be worth more than his spot in the rotation. Brent Suter emerged as a valuable up-and-down, swingman type in 2016, and expanded that role in 2017. Chase Anderson and Jimmy Nelson looked like low rotation innings eaters, at the very least, until mechanical changes in delivery timing (Nelson) and pitch sequencing adjustments (Anderson) catapulted both starters to the top of the National League.

If the Cubs opened a -90 run door for the Brewers, Milwaukee entered that door with a 35 run improvement of their own, closing some of the gap between the clubs (the remaining gaps would be largely explained by the exceptional Cubs offense, but the Brewers stuck around thanks to their equally exceptional bullpen).

In the middle of the season, I studied 2011-2016 runs prevented progressions for National League rotations, and found that a typical pitcher working in two consecutive seasons would see their production fluctuate by approximately 57.0 Innings Pitched and 12 runs prevented. Granted, this was only the average fluctuation; more extreme fluctuations like those from Jon Lester or Jimmy Nelson would not necessarily be uncommon even if they were surprising. At the very least, the 2017 season demonstrated how rotational fluctuations can help to define the fate of a ballclub simply when the same cast of characters are kept around (again, these rotational fluctuations are calculated without any consideration to additions or subtractions in personnel).

For the Cubs, they likely learned a lesson that their large payroll capacity can readily solve, and pending free agency from a couple of their declining options will help them make that decision. Chicago largely began answering this question when they unloaded prospects for the midseason acquisition of Jose Quintana (84.3 IP, 6 runs prevented in Lakeview). Milwaukee, on the other hand, must heed the warning of the 2017 Cubs, and look at their own internal fluctuations for clues about building a successful 2018 rotation.

• First, were the positive steps of Anderson and Nelson missed entering 2017, or were the pitchers expected to take steps forward? This will be a crucial test of the club’s pitching approach with their internal analytics and their on-field coaching staff. If the Brewers were working with both pitchers on adjustments and did not expect either to move forward, the club must investigate these lessons to make better forecasts for the 2018 rotation.

• Second, were the overall forward steps of the rotation worthwhile enough to keep the same staff around? The Brewers already have a rotation spot to fill due to Jimmy Nelson’s shoulder injury (which the club is expecting to eat into a significant portion of the season), and they also have a decision to make about Matt Garza’s option. But, it is worth asking whether the club can expect to move forward by opening rotation spots for pitchers like Brandon Woodruff (43.0 IP, -1 Runs Prevented in his first taste of MLB action) or even Suter (who could serve as a season-opening 5th man while advanced minors options make their last adjustments before promotion).

Beware those fluctuations, and heed those forward steps by Anderson and Nelson: the Brewers contended in 2017 solely on the strength of their above average pitching staff. So the question remains, what will be the next step for this pitching system?

Photo Credit: Benny Sieu, USAToday Sports Images