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Where has Jake Arrieta's slider gone?

Jake Arrieta looks to get back on track against the Pirates. AP Photo/Mark J. Terrill

After a string of starts that have him appearing mortal, Jake Arrieta faces a familiar foe Friday: the Pittsburgh Pirates.

With the Chicago Cubs slumping and playing their worst baseball as the All-Star break approaches, can Arrieta turn it around?

Reminder of who Arrieta can be

Since June 1, Arrieta has a 4.05 ERA and a 1.44 WHIP. He has walked 12 percent of batters faced in that span and has allowed a third of batters faced to reach base against him.

Despite that, he still entered Wednesday with the third-best ERA among starters.

So what’s wrong?

In the last preview blog on Arrieta, we mentioned he could stand to be more aggressive when he gets behind in the count. While this remains true, Arrieta’s biggest problem lately might be a lower spin rate on his slider.

Arrieta has experienced a lower swing rate, miss rate, chase rate and in-zone location rate with his slider in his last six starts in part due to this lack of spin.

The more a pitch spins, the sharper or more sudden its movement can be. Arrieta’s slider is spinning at nearly 200 fewer rotations per minute compared to what it was earlier in the season. That's roughly 80 percent of the spin he had in his first 11 starts.

This has led to less horizontal movement on the pitch in its last 40 feet, making it easier to pinpoint where the pitch will end up earlier in its flight path.

In simpler terms: the movement on his slider is down, and it is becoming easier to avoid chasing or missing the pitch.

Fixing it for his next outing

Arrieta is throwing his slider less frequently recently, which is a sign he’s already making adjustments. The good news for Arrieta is that his opponent Friday night is the Pirates, a team he has a history of success against. Since joining the Cubs, Arrieta has a 1.19 ERA and 0.74 WHIP in 10 starts against Pittsburgh.

If Arrieta’s slider still lacks spin Friday night and he relies on his fastball, that might not be a bad thing. The Pirates are 4-for-37 in at-bats ending in a fastball from Arrieta this season.

Arrieta has been vocal about his attempts to fix the issues that have plagued him recently. If he can get back the spin rate on his slider, he’ll be in a good spot to dominate on Friday night.