Jake Arrieta finished 2015 with a 9.28 K/9 and 1.89 BB/9 en route to the best second half in MLB history. The Cy Young winning righty took MLB by the reins and only allowed a .186 wOBA in the latter half of the year, eventually striking out 11 batters in the NL Wild Card game. Personally, I’ll be talking about those months *extreme Squints voice* for…ever.

But those days seem like they were long ago.

Since Arrieta wrote his name boldly across the broader sporting consciousness, the Cubs dove into two deep postseason runs and won the World Series, journeys that might have contribued to his latest woes and regression. Arrieta finished 2016 with a robust 3.12 ERA, but had a questionable 3.68 xFIP. And he’s heading into mid-June of this year with a 4.46 ERA and similar 3.60 xFIP.

Despite a high ERA this year, Arrieta actually is generating 5 percent more whiffs than his historical campaign, which has led to a 10 K/9. Even Arrieta’s walks are down from last year, too — 3.47 BB/9 to 2.6 BB/9. This all would suggest that the Cy Young winner is back to his 2015 days, but that hasn’t been the case due to an inflated home run rate and low grounder rate. Nevertheless, Arrieta is in the midst of reinventing his game, and, once numbers begin to stabilize, we could see him really start to take off.

Revamped Mechanics

Before this season, the pilates-loving pitcher had about two inches of separation between the horizontal release points of his slider and sinker. But once Arrieta’s started to throw his slider with less velocity last year, he ultimately produced 22 percent fewer whiffs. In other words, he was able to get away with the variation between his sinker and slider release point in 2015 because of pure stuff.

Encouragingly, the variation between the two pitches has been essentially eliminated this year. He’s throwing both out of the same tunnel. In fact, Arrieta’s sinker-slider release:tunnel ratio is now the fourth best in MLB. According to Baseball Prospectus, “this stat shows us the ratio of a pitcher’s release differential to their tunnel differential” and “smaller differentiation between pitches through the tunnel point [makes] it more difficult for opposing hitters to distinguish them in theory.”

The improvement is quite dramatic, as Arrieta ranked 68th in MLB just last year and 102nd in his Cy Young year.

Visually, too, it’s easy to pick up the difference. I highlighted the gap between his sinker and slider release points to emphasize. Notice how there is basically no yellow in the 2017 data compared to prior seasons.

Letting go of the baseball in the same tunnel has improved the swinging-strike rate on Arrieta’s slider to a level similar to 2015. Remember, he is throwing roughly 3 mph slower than 2015. The fact that he’s able to create more whiffs on the same pitches with less velocity is remarkbale.

Conclusion

Arrieta’s slider release point inconsistency was an issue in 2016 and correlated to less movement overall. A change needed to be made. Revamping his mechanics to the point where the difference between his slider and sinker release point is practically zero could be the change he needed. Consistent mechanics and a likely improvement in grounders means Arrieta’s best days could be ahead of him.