In the offseason, there were reports that the Braves asked for Carlos Martinez in a trade for Jason Heyward, only to be turned down and offered Shelby Miller instead. If these reports are true, then Shelby Miller and Carlos Martinez will always be linked, for better or worse, since the Cardinals evidently had a choice between the two on who to keep and who to trade. Here's a very early comparison of the two pitchers and their results so far in 2015.
Before I go into the data, I think it is very important to point out that it would be idiotic to draw sweeping conclusions about either pitcher based on what they have done so far in 2015. Neither pitcher has started ten games yet this year, and there are still a lot of small sample size issues present in their 2015 stats. It is also important to keep in mind that Shelby Miller will not be a free agent until after the 2018 season, while Carlos Martinez is under team control for a year longer. It will extremely difficult to judge the Jason Heyward trade and the decision to trade Shelby Miller (instead of Carlos Martinez) until we see how Miller and Martinez do in their remaining years of team control.
With those disclaimers out of the way, here are the early season stat lines for each pitcher, courtesy of Fangraphs.
Up to this point, Shelby Miller has, without a doubt, gotten better results than Carlos Martinez. He has a much lower ERA and FIP, a higher WAR, and more innings pitched. He's been better than a lot of pitchers, in fact, as his 1.33 ERA is the best in all of baseball. Because of his sparkling ERA (and his 5-1 record), many pundits are already proclaiming him to be the early favorite for the NL Cy Young Award.
While I agree that Miller is off to a fine start, I find this last assertion to be laughable. He is currently 13th in the NL in WAR and 16th in FIP, and these metrics are a much better indicator of a pitcher's performance than ERA. Looking at his peripherals, it's easy to why Miller has outperformed his FIP by so much this season. FIP adjusts for defense, batted ball luck, and sequencing, and Miller has had a lot of help from two of these three factors.
While the Braves defense hasn't been all that great so far this year (20th in baseball, according to Fangraphs), Miller has been incredibly lucky with batted balls and sequencing. Hitters have a .183 BABIP against Miller, far and away the lowest in all of baseball (the next lowest is Zach Greinke at .217). In addition, Miller is third in baseball with a LOB% of 88.8, less than one percent behind the league leader. While I hate to explain Miller's excellent start by simply saying that is mostly due to luck, it is impossible to deny that luck has played an enormous part in his great start to the season.
Martinez has also outperformed his FIP, though not by nearly as much as Miller. His BABIP is about where it should be, but he has been helped by a high LOB% and a good Cardinals defense (7th in baseball, according to Fangraphs). Perhaps the most interesting number on Martinez's stat line is his xFIP of 3.56, which is actually better than Miller's. xFIP is like FIP in that it adjusts for defense, batted ball luck, and sequencing, but it also adjusts a pitcher's HR/FB rate to league average. For this reason, xFIP is helpful metric in predicting a player's performance going forward.
So far, Martinez has a ridiculously high HR/FB rate of 20.6 percent, while Miller's is a much lower 6.4 percent. The league average this year is 10.6 percent, suggesting that Miller and Martinez should see some regression as the season goes along. All told, Martinez should, in theory, be slightly better than Miller going forward, given equal defensive help, batted ball luck, sequencing, and home run luck. The ZiPS rest of season projections for each pitcher seem to confirm this idea.
Going forward, a choice between Shelby Miller and Carlos Martinez would be difficult, but I'd still probably go with Carlos Martinez. In addition to looking at the projections, I think it is helpful to remember that Martinez is a year younger than Miller and has an extra year of team control.
In fact, I would argue that very little has changed with regard to the Miller/Martinez comparison since the offseason. Back in November, Bernie Miklasz wrote an excellent piece discussing the choice of Martinez over Miller, and there isn't too much that was written then that doesn't still ring true today. When talking about two pitchers who are 23 and 24 years old, it is important to look at each pitcher's upside, and Martinez still has more upside than Miller. The Cardinals certainly factored this, among other things, into their decision, and given the information we have today, I still think that they would make the same decision that they did in the offseason.
While this answer may not be satisfying for the impatient, short attention span, talk radio type people, it is probably the most we can say at this point. And for anyone who wants to criticize the Cardinals for being too high on Martinez, keep in mind that the Braves asked for Martinez instead of Miller. (Credit to Bernie Miklasz for making this point earlier in the week.) Clearly, the Cardinals aren't alone in their love for Martinez, and eight starts should not drastically change their opinion of him. The Cardinals had good reasons for trading Miller instead of Martinez, and they should not have any major regrets about the trade just because of how the 2015 season has started.