More Fastballs, Different Fastballs for Rubby

On Tuesday, Rubby De La Rosa started for the Diamondbacks. It was Arizona’s second game of the season. That made De La Rosa the D-backs’ number two starter, kind of. At least that’s how people thought of it, and when they did, a lot of them said, “hey, Rubby De La Rosa is our number two?” to which others responded, undoubtedly, “I guess,” because how could anyone really be sure? A number two starter is supposed to be good. Rubby De La Rosa really hasn’t been, so you can see where the confusion lies. And one of the reasons he hasn’t been good is because he doesn’t really mix up his pitches. That can be problematic.

Big league hitters are good and even though hitting a baseball is exceedingly difficult, they manage to do it pretty well. That’s why they make the big bucks, as they say. Pitches work on a sort of double axis scale. On one axis is a batter’s perceived difficulty in hitting a pitch. The other axis is the pitcher’s perceived ability to throw said pitch for a strike. It’s a sort of yin and yang relationship for most pitchers, De La Rosa included. He’s struggled with his pitches, though, which is why he’s not very good. I’m not sure if it’s too much yin or too much yang, but I have a pretty good idea it’s too many fastballs. Yes, the bulk of fastballs have been a problem.

In 2014, De La Rosa threw some sort of heat 67% of the time. You’re probably proficient at math, but just in case, that means that two out of every three pitches was a fastball. Now I don’t know about you, but with that kind of overwhelming tendency, it’s not inconceivable to think that hitters sat back and waited for a fastball. Given the information above, that would be a pretty worthwhile strategy. And if you have an idea of the velocity a pitch is coming, you can probably start to get a feel for the timing needed to hit said pitch. Relying on that many fastballs signals a problem in and of itself.

But De La Rosa tries to at least mix it up by using two different kinds of fastballs, a four-seamer and a two-seamer (sinker). Although they are definitely different pitches, the results were pretty much the same in 2014. Take a look for yourself.

Most of the above information would paint the picture that the two fastballs were nearly identical, at least from an outcomes-based perspective. The value of the pitches was at least somewhat split where the two-seamer outpaced the four-seamer over the course of 2014, although neither was actually “good”. But, De La Rosa threw the two seam fastball far less. So it would stand to reason that he’d throw it more frequently in 2015. Lo and behold, take a look at the numbers from his last spring start:

We see a clear move towards more two seamers and away from so many four seamers in his last start of Spring Training. And, sure enough, we saw it on Tuesday night, too. There are 11 fastballs that went unclassified, but if we pepper them in at the confirmed rate, we see a clear change from last season.

So, yeah, there’s been a change in Rubby’s fastball usage. Unfortunately, it wasn’t effective. Of the confirmed fastballs we saw, here’s how they worked out:

That’s not a real good rate of strikes considering these are De La Rosa’s bread and butter. They also yielded six hits and eleven outs, all of the outs that De La Rosa recorded. Now, it’d be easy to say, “hey, that’s how he got guys out,” but to that I’d reply, “hey, he gave up six runs in four and two-thirds innings.” Recording outs is good and all, but only if you don’t let guys score. He let guys score.

And that leaves us with an interesting dilemma. Where does he go from here? True, it was just one start and the Diamondbacks have every reason to continue using him, but by throwing so many fastballs, one has to wonder if hitters can literally just sit on them. Case in point: with two down and a runner on second, Buster Posey expected a fastball from De La Rosa to begin his at-bat. He got one, a two seamer, and didn’t miss it.

Later, in the fourth, Brandon Belt was up in the count and had a high probability of receiving the heat. He got it, another two seamer, and drove in a run.

That pitch wasn’t particularly bad, it was down and away, but by being able to time the pitch and know what to look for, Belt simply hit it where it was pitched and drew the Giants within a run. Given the rate at which De La Rosa throws fastballs, why would he have been looking for anything else?

Now, Rubby threw a handful of good sliders and has a mediocre changeup or two, but until he’s able to mix these in more effectively, and more frequently, hitters will still sit fastball. And that’s bad for the Diamondbacks. Fastballs aren’t hard to hit for major league hitters. Even if they’re reasonably well-located and in the mid-90’s, if they’re expected, they get hit. He’s going to need to establish something else to avoid becoming a reliever, something I, and many others, have projected. He should get plenty of chances given the competition, but should he not improve by June, De La Rosa could find himself out of a rotation spot.

That’s not what you want to hear about your “number two” starter.