Just before the season, I unveiled a system for rating starting pitchers by tiers and focused the method strictly on those who earned one of the 30 coveted Opening Day starts across baseball. Though we didn't get into the overall results at that time, that exercise drew upon a mere subset of the data: All starting pitchers were in fact rated, and all were slotted into various tiers against each other.
With the teams on their annual midseason break, a little over half of the schedule has been played (54.6 percent, in fact). That makes it a good time to update the numbers and see who has changed tiers, either to the positive or negative. It also lets us take a snapshot of the first half in starting pitching across baseball.
The tiers are built according to a metric called ACE score, determined by a methodology identical to that laid out in the previously linked piece. All starters are slotted against all other starters since the beginning of the 2014 season, though the tier lines are drawn just for those active in 2017. The general categories being rated are performance, durability, consistency and dominance.
There are six tiers, which can be roughly defined as such:
Bound for Cooperstown
Front of the rotation
Solid No. 2 or 3
Solid No. 3 or 4
Just a guy
Since there are different ways to approach the data and we don't want to dump the whole thing on you, let's go through it FAQ style.