Get Well Soon, Chris Tillman

Chris Tillman served admirably as the Orioles' de facto ace in 2016, but the team will be without him for a little while this season. Shoulder discomfort has kept Tillman out of spring training thus far, and he expects to resume throwing next week. Buck Showalter has indicated that he does not expect Tillman to pitch in the majors in April, and if I've learned anything from pitching injuries, I am afraid to be that optimistic.

Sitting Tillman early in order to let him fully heal and remain effective throughout the season rather than flopping on and off the DL is probably the safest course of action. With that in mind, we should temper expectations for the beginning of the 2017 season. The Orioles hardly have a full starting rotation, much less depth beyond the five pitchers that will regularly work as starters. The pitcher (or pitchers) that will assume Tillman's slot in the rotation in his absence are likely to be worse than him, which makes it harder for the team to win at the same rate they would with a healthy Tillman on the mound.

To estimate the quality of team that will take the field with a replacement pitcher on the mound, and how it compares to the team that takes the field with Tillman pitching, I turned to Joe Peta's base runs team quality formula. This is the process by which we use the base runs formula to estimate how much a team should have scored and allowed given its performance offensively and on the mound, which I have used in the past to evaluate money lines on playoff games,

For this project, I used 2016 statistics to determine how many runs the Orioles would be expected to give up with Tillman pitching compared to how many runs a composite of possible spot starters (Mike Wright, Wade Miley, and Tyler Wilson were my possible replacements). Each of these pitchers had their performances prorated to a full season. Similarly, I prorated season-long performance from the expected nine starting batters to estimate the runs the Orioles would be expected to score.

Using each of these run expectancies in the Pythagorean win formula yields the following team quality matrix:

SP	Team	Base Runs FOR	Base Runs AGAINST	W%+
Tillman	BAL	797.6	679.9	57%
Tillman	BAL @ Home	861.4	679.9	61%
Composite Spot Starter	BAL	797.6	919.4	44%
Composite Spot Starter	BAL @ Home	861.4	919.4	47%

Chris Tillman is effective enough at preventing runs that a composite spot starter would lead a team that plays like a sub-.500 club, while Tillman would be pitching for what looks like a playoff team.

With 24 games in April, Tillman could be replaced by a spot starter in four or five games. In five games with Tillman on the mound, the Orioles should expect to comfortably win three games. Without him, the team would not be expected to win more than two. A small difference to be sure, but a one-win swing out of every five games adds up quickly in a division as competitive as the AL East.

Of course, the Orioles should not rush Tillman back before he's fully healthy and ready to pitch at a high level. Doing otherwise would risk further and more serious injury, and having Tillman pitch injured  would probably not yield results much better than his replacements.

Get well soon, Chris Tillman. If this team expects to compete this season in what looks like a tight AL East, it'll need you back, quickly, at full strength.