Strikeouts and Walks and Strikeouts vs. Walks
I felt like the best answer likely was a combination of strikeout rates, walk rates and the comparison between the two. Kershaw’s best seasons were also his best seasons in terms of raw strikeout and walk numbers and his K/BB ratio. From 2009-2011, Kershaw had the fifth-best K/9 amongst qualified starters at 9.51 with a BB/9 of 3.34, the 99th best mark amongst qualifiers.
His K/BB of 2.85, placing him right above aces Jon Lester and Max Scherzer, was good for 36th in baseball over this span thanks to a large number of strikeouts. But the contradiction between the high K rate and high BB rate meant that Kersh still had room to grow, and grow he did.
From 2012-2016, Kershaw had a 10.12 K/9 (6th in the MLB) and a 1.72 BB/9 (9th lowest in the MLB), which translated into a stellar 5.89 K/BB ratio, good for 2nd in all of baseball. This is the Kershaw we all grew to adore, the Kershaw with impeccable control and nasty stuff to boot, the Kershaw who in 2016 walked 11 while striking out 172, a historic margin.
Did this dominance of the strike zone continue into the 2017-2019 post-prime era? Is it what, at least in part, has kept him successful? From 2017-2019, Kershaw has posted a lower K/9 than both Rich Hil and Kenta Maeda, dropping down to 27th in baseball with a 9.32 K/9. In the walks department, Kershaw has remained elite, and in fact has further separated himself from the field, as his 1.58 BB/9 is the best mark in baseball over this span amongst qualified starters. Thus, Kershaw’s 5.89 K/BB from 2017-2019 is the exact same as his 2012-2016 mark.
So in summary, his strikeouts have remained relatively constant and his walks have actually improved in recent years. This for me rules out the idea that he has lost control and lost his stuff, at least in terms of the results. So what is causing Kershaw to fare worse in recent years than in the past?