Jake Arrieta is throwing slower this year, but velocity isn’t the only facet of his pitch repertoire that’s changed. The former Cy Young winner is working an unfamiliar portion of the strike zone, much to the discontent of teams that now have to throw away their past scouting reports.
Watching the ace paint the outside portion of the zone was like observing Caravaggio delicately applying his chiaroscuro technique to the canvas. Arrieta mastered the art in 2015 when he only walked 1.89 batters per game, but failed to mount such a renaissance the following season when his walk rate doubled.
Rather than board and brush, a pitcher’s art is best illustrated by heat maps. The first image below represents Arrieta’s 2015 location on the edges, and in it you can see how the darkening shades of red are focused directly on the lower-right portion of the strike zone. In the second image, which comes from 2016, the locus has expanded to spread across the lower fifth of the strike zone, suggesting worse command. Of note, these maps only include pitches that were defined as “on the edge” by Baseball Savant.
So far this season, Arrieta has strayed completely from the strategy that led to both historical pitching stretches and lengths of spotty command. Nowadays, the pilates-loving pitcher attacks righties by jamming their hands, not by freezing them on the outside portion of the zone. Even absent any real context, the differences between this map and those above are obvious.
Why is Arrieta changing the way he attacks batters? Perhaps throwing to the third-base side of the zone keeps his mechanics in check. After all, he has to reach far across his body in order to dart pitches towards the first-base side. Or maybe the Cubs have data suggesting hitters will have trouble against inside pitches.
We can only speculate at this point, but the noticeable change in strategy has led to a robust 10.58 K/9 and 1.82 BB/9, both of which are better than his 2015 award-winning season.