One can use a traditional method to make the point that the Tampa Bay Rays have the best starting rotation in the major leagues. The Rays' starters lead the majors in earned run average by a healthy margin, despite Wade Davis getting tagged for five runs in 3 2/3 innings by the Red Sox on Monday night.
Leading rotation ERA
Another way to state the Rays' case is to look at SNLVAR (support neutral league value above replacement), a Baseball Prospectus metric that measures how many more wins a starting pitcher has provided over the course of the season than would a replacement-level player who could be claimed off waivers or purchased from a Triple-A roster.
A total of 57 major league pitchers have accumulated at least a 1.2 SNLVAR with just a little more than a quarter of the season gone. A pitcher who finishes with a 5.0 mark or better is considered to have had a very good season. The Rays have the only rotation in which each member has at least a 1.2 SNLVAR.
The Rays' SNLVAR
The teams that come closest to matching the Rays' rotation depth are the Giants, St. Louis Cardinals, San Diego Padres, New York Yankees and Chicago Cubs. Each has four starters with at least a 1.2 SNLVAR.
Here is how those teams' rotations break down:
Giants: Lincecum, 2.5; Sanchez, 1.9; Zito, 1.8; Cain, 1.5; Todd Wellemeyer, 0.2
Cardinals: Jaime Garcia, 2.4; Adam Wainwright, 2.1; Chris Carpenter, 1.6; Brad Penny, 1.2; Kyle Lohse, minus-0.4
Padres: Clayton Richard, 1.9; Mat Latos, 1.9; Wade LeBlanc, 1.4; Jon Garland, 1.4; Kevin Correia, 0.4
Yankees: Andy Pettitte, 1.9; Phil Hughes, 1.8; CC Sabathia, 1.2; A.J. Burnett, 1.2; Javier Vazquez, minus-0.1
Cubs: Tom Gorzelanny, 1.3; Randy Wells, 1.3; Ryan Dempster, 1.3; Carlos Silva, 1.2; Ted Lilly, 0.5
All good rotations, to be sure, but none quite as deep as the one the Rays spin through every five games.
However, there is reason to believe the Rays' rotation can't keep up quite the torrid pace it has been on through the first 45 games of the season. Tampa Bay's starters rank seventh in the majors in SIERA (skill-interactive earned run average), which estimates ERA through walk rate, strikeout rate and ground ball rate while eliminating the effects of park, defense and luck. Thus, we can expect some regression to the mean by the Rays as the season plays out.
SIERA vs. ERA
John Perrotto is editor-in-chief of Baseball Prospectus.