Jake Arrieta is doing good at the pitching things. As of this morning his ERA is a sparkling 2.09. And his FIP and xFIP suggest that's a result of good pitching rather than just a run of good luck.

His current ERA is a full two runs lower than his career mark (4.93). So, what's going on? How has Jake converted himself from a guy that bounced between the fifth spot in the rotation and Triple-A to what looks like a long-term piece? (Arrieta will not be a free agent until 2018.)

The Texas-bred fireballer has always had good stuff. His average fastball/sinker speed is a heavy 93, which means he frequently touches 94 and 95 with it. He's got a power slider that averages 88 mph, too.

For all that stuff, you've always wanted to see Arrieta get more strikeouts. After racking up 268 Ks in his first 263 innings of pro ball (A+ and AA mostly), his K-rate was closer to 7 per 9 IP for the next several years. And he walked too many guys for the Ks to much matter. Here are his K%-BB% rates since 2007: 1, 6, 15, 6. (That 15 might look nice, but it came with a bunch of home runs allowed, and a 6.20 ERA.)

The Cubs got Arrieta (AND Pedro Strop) for Scott Feldman last year. While he posted a decent ERA for the Cubs in 9 starts (3.66), the peripheral stats were ugly: a K/9 under 7, a BB/9 over 4, and 1.2 home runs allowed per 9. He basically survived on a .190 BABIP allowed, which is not sustainable in the long-term.

This year, Arrieta is allowing a BABIP of .325 -- potentially a bit unlucky. But he's also striking out nearly 1 out of every 4 batters he faces. His K% so far this season puts him in the top 25 of all pitchers with at least 40 IP.

So what's happened? The velocity has always been there, and he hasn't found an extra bit of juice this year. The difference, it seems, is in the quality of his breaking pitches.

P.S. -- NOW IS A GREAT TIME TO THANK FANGRAPHS AND BROOKSBASEBALL FOR PROVIDING PITCHING DATA SO THAT I MIGHT ANALYZE IT. THANKS Y'ALL. OKAY BACK TO THE STORY NOW.

Jake Arrieta is missing more bats with his curve ball, slider, and most notably, his change-up. From 2007 to 2013, Arrieta got hitters to whiff at his change up about 1 out of every 10 times he threw it. So far this year, he has 7 whiffs on 37 change-ups thrown -- that's nearly 1 whiff on every 5 pitches.

Of course it's a small sample size, but the early returns are great. And it may be the key to helping Jake figure out left-handed hitters, who have always hit better against him than righties. He has used his change up exclusively against lefties so far this season, with great results.

He's also been leaning more and more heavily on his slider this year. On June 3 against the Mets, it was his second-favorite pitch of the day (he threw it 27 times); on June 8 against the Marlins, Arrieta threw his slider more than any other pitch (32 times).

Arrieta has been able to throw more sliders because he's developed better command of the pitch (this past offseason? this year?). From 2007 to 2013, 40 percent of the sliders Jake threw went for balls. So far this year, that rate is down to 30 percent. He's getting more whiffs, fouls, and ground balls off of his slider this year compared to prior seasons, to the tune of about 10 percent.

From looking at his stats, I get the feeling that hitters used to be able to look for fastball strikes from Jake, and tended to lay off his breaking stuff unless it was grooved. Now that he's throwing in the zone more often with his slider and curve ball, hitters are having to swing at those pitches, no longer able to look for just one offering (hard stuff).

I'd say Arrieta's ERA will climb over the remainder of the season, mainly for one reason: he's going to give up more home runs. (He's allowed just one so far this season, off a slider.) But the ingredients are there for him to be a much-improved starting pitcher over the next several months. He has the raw stuff to be a top-of-the-order guy; we'll see if he can continue to get the results to match that lofty potential.

@AJWalsh08

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