jake arrieta cubs road blueThere is a BP article by Rob Mains that you must read if you are a Baseball Nerd.

It’s a look at some apparent league-wide changes in how batters are approaching pitchers who aren’t in the strike zone all that much – pitchers who have relied for years on getting hitters to expand the zone, so to speak, generating whiffs and weak contact. The shift this year in discipline has been notable – it’s the largest shift in that direction in at least a decade – and it appears to really be harming pitchers who had previously worked extensively outside the zone (Francisco Liriano has been the most famous of these types of pitchers in recent years, and he is absolutely being crushed by this shift in approach).

There are a ton of interesting angles to take with this train of thought, but for a quick hit, it immediately made me check to see where Jake Arrieta falls on the spectrum. When looking at where he was in the past and then this year, and then particularly his last four ugly starts, you definitely can see how much his breakout in 2014 and 2015 was aligned with a tremendous shift in how much he was in the zone and how much he was getting guys to swing outside of the zone.



A few notes for the chart to provide some context: 2014 was Arrieta’s first full year with the Cubs, and the start of his breakout; league average in 2015 in these three numbers were: 44.7 Zone%, 66.9 Z-Swing%, and 30.6 O-Swing%; and the last column is the one that jumps out at me within the context of hitters swinging less around the league at pitches outside the zone.

ARRIETAZone%Z-Swing%O-Swing%
201246.056.128.8
201345.960.829.5
201443.661.633.0
201544.163.034.2
201644.464.629.8
Last 4 Starts43.570.427.8

As you can see, the extent to which Arrieta was getting batters in 2014-15 was absolutely night and day from his time with the Orioles. The reason it worked is because his command had become so strong that he could put pitches exactly where he wanted them, leaving batters to try and do whatever they could with whatever he threw (wherever he threw it – given his stuff and velocity, good freaking luck).

This year, however, there’s been an enormous shift in how often batters are swinging at his pitches out of the zone (back to where he was with the Orioles), even though he’s in the strike zone roughly the same amount as he was the last two years. Compounding the problem, when he is in the zone, batters are swinging more often than ever (those tend to be the best pitches to hit, and you’d rather they didn’t swing, of course, because those are strikes).

Obviously we know this all ties back to Arrieta’s command at some level, but it’s not quite as simple as saying “Jake Arrieta is throwing too many balls, and it’s causing him problems.” That’s clearly not it.



There’s a wormhole here if you want to go down it, and one of the places it’ll quickly take you: part of the “problem” for Arrieta this year is that batters have stopped swinging so often at pitches outside the zone, which means those pitches don’t become strikes (more walks) or weak contact (at bats become longer and rate of hard contact increases). Some of that is on Arrieta’s command. Some of it, however, appears to be a league-wide change at the plate, responding to pitchers who work a lot outside the zone. It makes you wonder if this is what it looks like when greater readily-available data creeps into the game at the player-implementation level.

This is remarkable stuff, and you should really, really read the BP article so that you can go down your own wormhole.


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