Major Red Sox Pitching Trends That Will Determine Their Postseason Fate

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The Boston Red Sox's pitching staff was among the best in the American League in the second half of the season, leading the Junior Circuit in fWAR (11.5) between the rotation and bullpen, behind only the Dodgers in MLB. While the team has spent most of September with offensive problems, averaging 3.0 runs per game, the pitching has maintained the competitive pace.

Although pitching will not be the Red Sox’ biggest problem heading into the Wild Card Series against the Yankees, here are some interesting trends from the second half of the season that we should keep in perspective.

Brayan Bello Closed the Season On A Heater

Brayan Bello is one of the pitchers who has closed the season best on the Red Sox's staff, especially since he returned from Triple-A and began pitching on July 12. In 12 of his 14 appearances during that span, opponents have scored one run or fewer against him. During this stretch, only Payton Tolle (2.3) and Sonny Gray (1.6) have recorded a better fWAR than Bello (1.2). In fact, he has been much more dominant in his last four appearances, pitching to a 0.48 ERA and 2.08 FIP with 22 strikeouts and only three walks in 18 1/3 innings. The only run he has allowed came on a home run by Jonathan Aranda on September 19 in his best outing of the entire campaign, featuring eight innings and 11 strikeouts.

The key point of the dominance has been the effect of his breaking balls, which have generated more whiffs, raising their rate from 40% to 45.8%, between August and September. In addition, his opponents’ Perfect Contact rate went from 10% to 0%.

His fastball is also starting to shape up; part of the process has been in the improvements to his vertical movement. After falling to 10.2 IVB in June, his worst mark, he is at 12.6 so far in September. However, although he has had a small sample, hitters are still batting .350 (7-for-20) against his fastball, including the only home run he allowed during the month.

Jake Bennett’s Breaking Balls Have Stopped Fooling Hitters

Jake Bennett found a better version of the sinker in this second half of the season, reducing his batting average allowed from .235 to .210 and improved his strikeout rate from 17.6% to 26.6%. But the rest of the arsenal does not show the same progression in dominance. The whiff rate of the changeup, his main weapon, fell slightly from 33.8% to 27%, while on the breaking balls, competitive swings rose to 100%. That is a signal to follow, since Bennett has gone through many innings this season surviving because of hitters’ problems identifying his pitches. His Flawed Swing rates of 18% with the cutter and 13% when he throws the curveball carry the great weight of his repertoire.

Now, a key point about the contact he is allowing in this second half of the season is that opponents raised their over contact rate, increasing from 28% to 42% (i.e., how often they swung over the top of the ball). In part, other metrics show that they are getting to his breaking ball, but they are often hitting ground balls.

Ranger Suárez's Fastballs Became Too Hittable

The main signal with Suárez is in his fastball. Competitive swings increased from 80.9% to 94.1% in the second half, his whiffs decreased (from 12.7% to 11.8%), while his perfect contact rates practically did not change.

The result has been a jump from opposing hitters against the pitch, from a .223/.255/.320 slash line to .361/.623/.412 during this second half of the season. Suárez will have to work on his command and find the corners again, since hitters of both profiles are destroying his command mistakes when the pitch hangs in the upper part of the zone.

Tyron Guerrero Needs To Trust His Stuff Against Right-Handed Batters

Tyron’s season has been a great story of overcoming adversity as one of the key pitchers in the Red Sox's bullpen. However, he has not been able to control his problems against right-handed hitters, allowing a .318 average after limiting them to just .205 in the first half of the season. Guerrero’s K% has also fallen dangerously from 21.4% to 13%. He has only two pitches against righties, featuring his sinker 82.2% of the time and sometimes tossing his slider in the mix.

Throughout the season, the vulnerable point has been his battle to limit contact, as righties have hit .299 with a .358 slugging percentage against his sinker. The exit velocity of the 58 balls put in play is 81.9 mph. With that exit velocity, his opponents are averaging a .260 xBA, so I don’t need to tell you that they have had a little bit of luck. In contrast, Guerrero’s slider remains sharp, limiting righties to just a .125 average and .188 slugging percentage. Perhaps a better mix of his two primary offerings will yield better results (or at least combat some of that poor fortune).