Entering the 2015 season, the overwhelming opinion was that Clayton Kershaw was the best pitcher in baseball, and he was rated as such in Bill James' starting pitcher rankings. This is for good reason, of course; he was coming off three Cy Young Awards in the past four seasons, including each of the past two seasons, in which he posted ERAs of 1.83 (2013) and 1.77 (2014). This season, Kershaw's major peripheral numbers, such as his strikeouts per nine innings (11.9) and walks per nine (1.7) are as strong as they've ever been, but his resulting 8-6 record and 2.51 ERA seem almost disappointing compared to the amazing standard he has set for himself.
Los Angeles Dodgers teammate Zack Greinke has lived in Kershaw's shadow since joining the team before the 2013 season, despite being one of the best pitchers in baseball in his own right. But this year, Greinke has seized the spotlight. He has a 9-2 record with a 1.30 ERA that tops all qualified MLB starters, a full 79 points ahead of second-place Max Scherzer. Greinke's current 43 2/3-inning scoreless streak is the longest since Orel Hershiser pitched an expansion-era-record 59 scoreless innings in 1988, and he has vaulted from 10th in Bill James' rankings at the start of the season to third.
The strange part about Greinke's increased success this season is that, similar to Kershaw's so-called decline, it has come without major changes in his strikeout and walk rates. In fact, Greinke has struck out just 8.02 batters per nine this season, more than one fewer batter per nine than he did a year ago. So what gives? It seems likely that Greinke has been far more fortunate than Kershaw with respect to elements outside of their control, but it's also probable that differences in their command and their own defensive play have also contributed to their results. Let's have a look:
'Luck' factors
The most effective ERA predictors are based primarily on pitcher-controlled outcomes such as strikeouts and walks. The prevailing theory is that pitchers have limited control on the clustering of hits and outs, as well as limited control as to whether balls even become hits or outs once they've left the bat.