Clay Buchholz, Matt Moore and Matt Harvey have all had incredible starts to the 2013 season and are receiving a great deal of attention. But none of those pitchers led baseball in ERA in April. That honor goes to St. Louis Cardinals starter Jake Westbrook. The 35-year old right-hander posted a 0.98 ERA in the first month of the season and his current 1.07 ERA is the second-best mark in baseball.
This early in the season, how much stock can we put in Westbrook's performance?
Over the course of a month, players have strange and unsustainable boosts in their performance, while others go through monthlong slumps that result in fans breaking out their pitchforks and torches early and often.
To sort through this, analysts use metrics such as pitcher's batting average on balls in play (BABIP) or strand rate to attempt to analyze how "real" a pitcher's ERA has been and where it may move going forward in the season.
Baseball Info Solutions takes this one step further. We track each batted ball (including home runs) and can estimate how "lucky" a pitcher is getting. These batted ball times can then be combined with the tracked location to create an expected run value for each ball in play. Comparing the actual number of runs a pitcher has given up on balls in play with the expected number of runs given their batted ball distribution, we can get a much better idea of how real a pitcher's ERA has been than simply using BABIP or strand rate.
I compared the expected runs and actual runs given up on balls in play for every pitcher who has allowed at least 80 balls in play in 2013 (through Thursday) to come up with a list of the five luckiest and unluckiest pitchers thus far in 2013 in terms of ERA.