Swinging strike rate, or the percentage of pitches that result in a swing and a miss, is one of the most powerful tools for any fantasy player to utilize when attempting to evaluate starting pitcher performances. The calculation of the metric is incredibly simple once you understand what it's measuring:
SwStr% = Swing and misses / Total pitches
Sports Info Solutions and PitchFX both track and provide the inputs for this metric and the stat has been publicly accessible for nearly a decade. The advent of swinging strike rate was a breakthrough for fantasy baseball analysts and those who project player performances because it was the first time we could begin quantifying how dominant a pitcher was relevant to others in the league. As such, swinging strike rate became the best metric we had for predicting and correlating a pitcher's raw strikeout rate.
As time went on, it became evident that relievers and starting pitchers had two very different baselines when it comes to SwStr%. League-wide average for relievers is 11.8%, while starting pitchers is 11%. As you might expect, swinging strike rate has been trending upwards in recent years, following the overall trend in major league baseball as the game shift closer towards the three true outcomes (K, BB & HR).
When applying SwStr% to try to find an edge, you have the separate the "well duh" results (i.e. Gerrit Cole) from the more interesting values (i.e. Josh Staumont). Notably, pitchers who have year over year deltas in their rates are often a nice starting point for your analysis because they cause you to ask the question "how?". Did they change their pitch deployment? Did they develop a new pitch? Were they injured?
Additionally, swinging strikeout rate is a great litmus test to validate whether large swings in a player's actual strikeout rates are justified or potentially under- or over-stated. As a rule of thumb, a pitcher with a league average strikeout rate of 23% would generally have an 11% SwStr%. If their actual strikeout rate was lower than that, the SwStr% would indicate that his strikeout totals may be under-stated and vice versa.
To help get the conversation going, join Lou Blasi and I will dive into Swinging Strike rate on SiriusXM Fantasy Sports Radio this Saturday from 10AM - 1PM ET. Tune in as we break down the players below. In the meantime, get a head start by finding the pitchers with the great year-over-year gains in SwStr% from 2019 to 2020.