In recent years, we have seen numerous examples of postseason teams succeeding in large part due to a deep bullpen. With the growth of analytics and the spread of ideas like the times through the order penalty, managers have gotten smarter and seem to have a better (but still imperfect) understanding of when to remove starting pitchers and how to optimize reliever usage. There are often benefits to having a quick hook with a starting pitcher in the postseason, but the success of this strategy often depends on the skill level of a team's lesser relievers. Managers are still cautious about taking late-inning relievers out of their preferred roles, which means that the middle innings of a playoff game are often covered by a team's fourth-, fifth-, and even sixth-best relievers.
In their series against the Cardinals, the Cubs were very successful in getting contributions throughout their bullpen, especially from three former starting pitchers: Trevor Cahill, Travis Wood, and Clayton Richard. Combined, these three pitchers faced 27 batters in the NLDS, giving up six hits, two runs, no walks, and striking out eleven. Obviously, we are looking at a very small sample size here, but these contributions are still noteworthy because two of these players (Cahill and Richard) had struggled so much that the Cubs were able to acquire them for basically nothing, while the third, Travis Wood, was not good enough to stick as the Cubs' fifth starter, despite having multiple opportunities to do so.
Cahill has been the best of the trio, posting eye-popping strikeout numbers since becoming a reliever. He had been a full-time major league starter as recently as last year, but he had not been very effective for some time. Since April, he has been dealt from the Diamondbacks to the Braves to the Dodgers, appearing in the major leagues only with the Braves. He was signed by the Cubs on August 19th after pitching 34 1/3 innings at Triple-A for the Dodgers. He made 11 appearances for the Cubs at the end of the season, pitching well enough to make the postseason roster.
Since moving to the bullpen, Cahill has seen a spike in velocity, as his sinker (his primary pitch) has averaged 93.2 MPH. (As a starter, his sinker never averaged higher than 91.1 MPH in any season of his career.) Cahill has also simplified his repertoire by eliminating his cutter, which he had thrown nearly a quarter of the time in his brief stint with the Braves this year. With the Cubs, Cahill has increased the use of his changeup to 26 percent, and this strategy seems to have paid off, as he has a ridiculous 34 percent whiff rate on the pitch according to Brooks Baseball.
Clayton Richard was acquired by the Cubs on July 3rd in a rare intra-division trade with the Pirates. Like Cahill, Richard's season was full of odd transactions, as he was designated for assignment twice by the Cubs (July 22nd and August 3rd) before being re-signed two days later when Rafael Soriano hit the DL. Richard used to be an effective starting pitcher for the Padres, but his career was derailed by shoulder injuries. While he hasn't put up eye-popping numbers with the Cubs, he has been moderately successful against left-handed batters in 2015, facing 67 of them and allowing a slash line of .234/.269/.266. In a bullpen dominated by right-handers, Richard has found a spot as a second left-handed option for Joe Madden.
The other left-handed reliever, of course, is Travis Wood, who came into the season as the Cubs' fifth starter. He lost his spot after seven starts and has made only two spot starts since then. Since being moved to the bullpen, however, Wood has been outstanding.
Wood pitched even better at the end of the year, allowing one run in September/October while striking out 23 and walking four in 16 innings. While Wood has shown a moderate platoon split throughout his career, he is capable of retiring right-handed batters as well, which is why his appearances are longer than those of a typical lefty specialist.
Like Cahill, Wood has seen a noticeable jump in velocity since moving to the bullpen. As a starter this year, his average fastball velocity was 90.1 MPH, and since being moved to the bullpen, his average velocity is up to 91.5 MPH. He has also changed his pitch selection as a reliever with more of an emphasis on his four-seam fastball.
What's interesting about Wood's pitch usage graph is that his increase in four-seam fastballs and decrease in sinkers began between May and June, which coincides almost perfectly with his mid-May switch to the bullpen and his subsequent run of success for the rest of the year.
It seems as though these kind of reclamation projects are starting to become the norm for the Cubs and pitching coach Chris Bosio. In recent years, the Cubs have been able to get the most out of pitchers like Scott Feldman, Jason Hammel, and Jake Arrieta, and each of these pitchers has had an enormous impact (directly or indirectly) in the success of the current Cubs team. (Feldman was traded for Arrieta and Pedro Strop, and Hammel, who is back with the Cubs, was part of the deal that brought back Addison Russell.) The Cubs are already well-known for their excellent core of young position players, and if they can continue to develop excellent pitching seemingly out of nowhere, they will be a scary team for years to come.
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