Jose Quintana’s K/9 and SwStr% Disconnect

Last week, I profiled Jose Quintana as a pitcher’s whose ADP and our auction value differed. In my analysis, I noticed that his swinging strike rate (SwStr%) and strikeout rate (K/9) didn’t move in tandem. Here are the pair plotted against each other.

And here are his historic values showing he doesn’t have a propensity to have a higher strikeout rate than his swinging strike rate suggests.

Quintana’s projections seemed based off his strikeout jump, not his swing-and-miss numbers. Steamer has him pegged for a 9.1 K/9 for 2018. Today, I’m going to look to see if just looking at strikeouts rates and not swing-and-miss totals is the correct procedure moving forward.

First, I need to clear up one misconception, the jump in strikeout rate without a SwStr% boost was not from a change in leagues. His strikeouts did jump from 9.4 K/9 to 10.5 K/9 while his SwStr% stayed almost the same going from 8.4% to 8.6%. The AL-based 9.4 K/9 would be a career high for him so the difference existed before the trade.

To find out the normal transition, I compared all starters who moved from one league to another since 2002. In total, 55 moved from the AL to the NL and 48 from the NL to AL. Here’s how the numbers changed.

On average, the pitchers moving to the NL saw their K/9 go a quarter to a half run higher. The swinging strike rate made a similar change with nearly a quarter to half percentage point change.

Getting back to Quintana, both of his changes are in line with the historic changes with his K/9 changing a bit more and his Swtr% maybe a bit less.

Now that the move can be removed as a factor, here is a plot of the K/9 and SwStr% numbers since 2014 for pitchers with 120 IP. Originally, I meandered down a path with values back to 2002 and found the difference between K/9 and SwStr% changing over time. The reason was a changing strike zone as outlined by Jon Roegele at The Hardball Times. The 2017 strike zone was most similar to the zones from 2014 to 2016 so I used these seasons.

While the r-squared is not 1.0, a .65 value is a decent amount of correlation. Using the above equation, normally a pitcher with an 8.4% SwStr% would have a K/9 of 7.1, not a 9.9 K/9. There is a reason Quintana’s difference sticks out because of the 480 pitchers in the sample, his varied the most.

Now, which value, as more weight the next season? Here are the top-twenty pitchers who had the biggest change and still met the criteria of 120 IP and a starter (GS/G >= 0.5)?

The pitchers who have the biggest disconnect between their K/9 and SwStr% keep their disconnected K/9 numbers going into the next season. For those who just want the short simple answer, they should expect Quintana to continue with the high strikeout numbers.

One obvious change is that the pitchers’ SwStr% jumped the next season putting it more in-line with their K/9. The near 1%-point change does not account for all the 0.5 point change in K/9. The difference averages out to 1.5 K/9. Just some change is explained.

I have a theory on why the difference is even more.

According to Baseball Prospectus, all of the catchers that were behind the dish for Quintana were markedly better than what he got from his primary catcher in 2016, Dioner Navarro. Even his secondary catcher from ’16, Alex Avila, was holding him back compared to his 2017 crew, which again included Avila once Quintana was traded. Avila’s framing took a big step forward from Detroit to Chicago, though that’s probably due in large part to the quality of arms throwing. At any rate, Q got framing bumps that no doubt helped his strikeout rate.

Jose Quintana’s strikeout and swinging strike rate don’t seem to jive. Don’t worry about the difference. Of the pitchers with the most extreme disagreements, the strikeouts rate is more predictive going forward with most of the gains sticking. The reason behind the gains staying is a not exactly known but they do continue. With pitchers normally keeping their gains, owners can pick up Quintana and expect him to keep his 2017 strikeout gains.