By now, most of us are familiar with Clayton Kershaw’s impressive 2015 campaign. He leads the league in fielding independent pitching, with a FIP and an xFIP that outstrip the average hurler by 44 and 47 percentage points, respectively. He strikes out a top-ranking 34 percent of the batters he faces while walking only five percent of them.
After a string of dominating performances in July, Kershaw has joined Zack Greinke and Max Scherzer as Cy Young candidates, with each of the three starters enjoying a 30 percent chance of winning the award. Altogether, this season is arguably the second-best of Kershaw’s career.
How has Kershaw amassed these extraordinary statistics? Naturally, there are many reasons for his ongoing success, but the most noteworthy is his curveball. While it has long been (in the immortal words of Vin Scully) “Public Enemy Number One,” you can make the argument that it is more lethal than ever.
Let’s start with how the pitch is being delivered. Based on data from Baseball Savant, we can analyze the average spin rate of Kershaw’s curveball over time and see its recent improvement:
In 2012 and 2013, the pitch spun a little under 1400 revolutions per minute. After climbing toward 1500 rpm last year, it has exceeded 1600 rpm this season — the highest in his career.
What’s the significance of this increase? As Jonah Pemstein notes, the more topspin a curveball has, the more it tends to drop. This chart from Brooks Baseball shows that Kershaw has indeed added extra downward movement to his pitch:
While an average curveball had a five-to-six-inch drop between 2012 and 2014, Kershaw was at 8.5. This year, he’s stretched it to a 10-inch drop.
The extra downward movement has allowed Kershaw to bury the curveball closer to the ground. If we compare his 2014 and 2015 heat maps, we find that the latter has a greater concentration of pitches right below the strike zone:
Specifically, in 2014, approximately 30 percent of the curveballs were located right below the strike zone. The frequency has grown to roughly 36 percent in the current season. It’s a positive development for Kershaw, who induces 59 whiffs for every 100 swings and allows a mere .081 lifetime batting average in this area.
With the curveball more effective than ever, Kershaw is putting it to sensational use. He has delivered it 18 percent of the time this year, up from 14 percent last year. During that same period, the pitch has raised its swinging-strike rate from 16 to 19 percent while reducing its contact rate from 64 to 58 percent. Moreover, Kershaw has increasingly finished off batters with it:
Overall, this year, opponents have earned just a .099 wOBA against Kershaw’s curve. It’s been the best pitch of its kind in the Majors. When the reigning Cy Young recipient and Most Valuable Player takes his most potent weapon to another level, it truly does seem criminal.