Pitcher Zach Stewart was acquired by the Boston Red Sox on June 24 in a trade with the Chicago White Sox, but it was not until Wednesday that he actually made his major league debut with his current employer. Based on the way he pitched on Wednesday against the Los Angeles Angels of Anaheim, the Red Sox no doubt wish they had postponed Stewart’s debut with the club indefinitely. Instead of rewarding his new team with stellar pitching, Stewart did the complete opposite and was completely ineffective during his short time on the mound.
Lasting just 3.0 innings, Stewart was so abysmal on the mound that he pretty much single-handedly put the game out of reach for the Red Sox. He cost the Red Sox even the opportunity at a chance for victory by allowing the Angels hitters he faced to knock his pitching around like he was throwing batting practice to them. Stewart allowed the 19 hitters he faced to post a batting line of .526 BA/.526 OBP/1.105 SLG with a .683 wOBA, making it incredibly easy to see how the Angels managed to score nine earned runs against him.
Even without the benefit of drawing a walk, the Angels hitters were able to hit their way on base, with an elite-level of power to boot, so successfully that Stewart just wasn’t up to the task of preventing them from scoring runs. Stewart also failed to strand almost any of the base runners he allowed, only putting up a pitiful left on base percentage of 13.9 percent.
All of Stewart’s poor pitching combined to leave him with a win probability added of -0.444, which was the lowest such mark by a Red Sox player in the game by far.
Although Stewart is not really a bad enough pitcher to give up nine runs in every start he has, neither is he good enough to be a productive starting pitcher in the major leagues. He has even struggled in his minor league career, making it extremely unlikely that he will ever help the Red Sox win games if he is kept in the starting rotation.
Over the past three seasons, Stewart has been exclusively a starting pitcher in the minor leagues, and he has been nowhere near dominant during that stretch. Each of those three seasons has seen his ERA around 4.00, which is much too high for a minor league pitcher that is trying to translate his pitching to the major league stage. Stewart will not be able to do anything but be ineffective against major league hitting. His ineffective performance on Wednesday was just the extreme end of the way in which he will be unable to prevent runs as a major league starting pitcher.