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jake arrietaEarlier this week, Jake Arrieta gave up four earned runs against the Giants, the most he’s given up in a start this year. But, you know, it really wasn’t a bad start. In fact, it was actually pretty good. A defender moved here, and a blooper that doesn’t bloop there, and Arrieta’s night against the Giants looks totally different. Sure, you can say that about a lot of starts, but he was pitching well, striking guys out, and not walking them. As far as a dink-and-dunk game goes, Arrieta got it pretty bad.

Which is to say … it’s encouraging!

It was Arrieta’s second straight excellent start after he took a week off to work on his mechanics. You don’t want to read too much into that, but I’ve always endorsed watching Arrieta closely. No one disputes that he’s got front-of-the-rotation stuff, but, like many pitchers with great stuff, a lack of command has held him back for years (and allowed the Cubs to get him). If he puts it together, though, the picture changes dramatically for the Cubs’ rotation heading into 2015.

And, consider this: Arrieta currently sports a 2.70 FIP and a 23.4% K rate. Both are great, but even they don’t stand out to me as much as his groundball rate: a robust 52.7%. If he qualified, that rate would put Arrieta in the 20/21 range in all of baseball.

Time and time again, we see pitchers coming to the Cubs and improving their groundball rates under the tutelage of pitching coach Chris Bosio (never let him go). For Arrieta, that 52.7% mark is nearly 10 percentage points higher than his career average, which is a remarkable shift. And, just as you would expect to see, he’s leaning much more heavily on his two-seamer/sinker this year than he did earlier in his career. That change in his pitch mix actually started back in 2013 … you guessed it, after he was traded to the Cubs.

How has that groundball rate already improved Arrieta’s results? Well, as you can surmise, groundballs do not become homers. And, if you’re a guy who frequently works with dudes on base (command issues), homers can be especially devastating. In his three previous years in the big leagues, Arrieta’s HR/9 and HR/FB were 1.58/15%, 1.26/14.5%, and 1.08/12.3%. Those are ugly, ugly numbers, and they were accompanied by groundball rates of 45.7%, 43.8%, and 40.4%.

It’s early, but fast-forward to 2014, and, accompanying the 52.7% groundball rate is a HR/9 of just 0.36 and HR/FB of just 5.6%. There will be some natural regression there (he did just pitch in Petco and AT&T Park), but it certainly looks like there’s an intentional shift here. And, so far, it’s working very well.

There’s another benefit in increasing groundball production for a guy like Arrieta, who has, in the past, battled efficiency issues. As we’ve seen with Jeff Samardzija, if you can couple great stuff (to break it out when you need it) with early sinkers in the zone, you may find yourself more able to go deeper into games: both because the balls in play can keep your pitch count down, and also because you will have shown fewer of your secondary pitches the first and second times through the order. Then, the third time through the order – and/or with runners on base – that secondary stuff could play up. It may seem strange to want to “turn” a pitcher with incredible raw stuff into a groundball pitcher, but you can see why the combination can be very effective. We’re seeing it this year with Samardzija.

Because of his pre-season shoulder issue, we haven’t yet seen this benefit for Arrieta actualized, because his outings have been artificially restricted in length. Over time, though, if the uptick in grounders is legit, we could see Arrieta going deeper into games – something he hasn’t done with much consistency over the course of his career.

Arrieta’s pitch mix and approach will be something to watch in the coming weeks. All of this could be a mere small sample fluke, or it could be the start of something very, very interesting.

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