The case for the Cubs having a six-man rotation in 2021

The 60-game MLB season played in 2020 meant, among other things, that pitchers threw fewer innings than ever in a calendar year.

Lance Lynn, now with the White Sox, led the major leagues with 84 innings pitched. Kyle Hendricks was third, with 81⅓ innings in his 12 starts, and the Cubs righthander led the major leagues in innings per start (6.8) for anyone who threw at least 60 innings (qualified starter).

But many starting pitchers threw far fewer innings than that. Leaving out the departed Yu Darvish, Alec Mills threw the second-most innings for any Cubs starter, 62⅓. Jon Lester, now also gone, threw 61. The next-most innings after Lester on the 2020 Cubs was 23⅓ — by reliever Jeremy Jeffress.

So it would seem to me that having a six-man rotation would be useful to the Cubs. Even with a (presumably) normal spring training this year, where starting pitchers slowly ramp themselves up from two innings to six or seven in a start, when this season (presumably) begins April 1, it will still have been 18 months since starting pitchers went through any sort of normal routine, the end of the 2019 season.

With the acquisition of Jake Arrieta, the Cubs now have enough starting pitchers to comprise a six-man rotation.

Kyle Hendricks is the obvious ace of the staff and he has averaged exactly six innings per outing over his 174 career starts.

But other projected Cubs starters don’t have a number like that.

Zach Davies has made 123 career starts and averaged 5.55 innings per start.

Alec Mills has averaged 5.47 innings per start in his 17 career starts. The same average holds true for Trevor Williams in his 94 career starts.

For Adbert Alzolay, the numbers are a bit skewed because he made a couple of starts during 2020 when he wasn’t expected to go more than three or four innings. He’s made just six career starts, averaging 3.94 innings per start.

Now add to that mix Jake Arrieta, whose 255 career starts instantly become the most on the staff. He’s averaged 5.88 innings per outing in those starts, and some of that is skewed by some really short outings in 2020.

A rotation including all six of these starters would give all of them more rest, allowing them to build up stamina. Eventually, later in the season the Cubs could go back to a five-man rotation and one of these pitchers (Mills, perhaps?) could become the long man/spot starter in the bullpen.

This sort of thing would be useful even though the Cubs have four scheduled off days in April and four more in May.

I’d arrange this rotation in the following order: Hendricks, Davies, Arrieta, Williams, Alzolay and Mills. The only real issue with it, other than the fact that no one on that list is a 95+ fireballer, is that they’re all righthanded. With Lester and Jose Quintana, the Cubs have had at least two lefties in the rotation since mid-2017. For now, they’ll simply have to do without a southpaw starter.

For more analysis on what a six-man rotation would mean, check out this Fangraphs article from last month by Ben Clemens. Among other things, the article notes that the Mariners have already decided to go that way and several other teams were in the process of considering it.

I think it’s worth doing for the Cubs, at least to start the 2021 season.