The Fallacy Surrounding Rubby De La Rosa’s Changeup

Rubby De La RosaI remember fondly watching Rubby De La Rosa’s 2014 debut against the Tampa Bay Rays May 31st at Fenway Park. He dazzled; not allowing a run to score in seven innings. What sticks in my mind more than anything, though, is how utterly ineffective Tampa’s lineup was against De La Rosa’s most highly-touted pitch, his changeup. Naturally, tweets from Red Sox Nation, myself included, far and wide were advocating the nastiness of his changeup. He utilized that pitch a bewildering 28.6% of the time in that contest, trailing only his two-seam fastball (32.4%) in terms of usage, yet, still, it couldn’t be hit.

Since then it seems because of the misleading eye-test, we’re trapped in this fallacy that his changeup is what it was game one and in the minor-leagues. However, that is so far from the truth, and as it stands, the right-hander’s changeup, in actuality, has been his worst pitch this season.

I don’t say that based on a deceptive small sample size assumption, but, rather, on cold hard evidence. According to Fangraphs, De La Rosa has thrown the pitch 278 times while hitters have clobbered the offspeed pitch for an imposing .945 OPS (.275/.383/.563 slash line).

To further emphasis its decline throughout the year and to get more than one source concurring the changeup’s inefficiency, I looked to the single best Pitch F/X data website, Brooks Baseball, for answers.

What I found was De La Rosa’s changeup was arguably at its best in his ’14 debut, as hitters only managed to churn a pedestrian .125 slugging percentage off it. But as the year persisted it just got worse, and hitters slugged .420 off it in June, a frightening .640 in July, and .500 in August.

All said, it’s not surprising to see De La Rosa going to the changeup less frequently and favoring the slider, a pitch that needs developing. Given Boston’s situation (no chance at reaching the postseason), it’s not a problem that Rubby has gone to his inexperienced pitch more often. Actually, it’s rather productive getting a feel for how to work that slider in against big-league hitters, whom, obviously, have an advanced approach at the plate. So, yeah, I like that he’s attempting to mix it in his arsenal more, but at the same time, I’m weary he’s not using the changeup enough, because, despite its performance, it’s his best pitch.

Take a gander at his per-month usage of the change correlated with his per-month performance.

Note (*All percentages are courtesy of Brooks Baseball

May (7 innings): Used the changeup 43.81% of the time and sported a 0.00 ERA in that span.

June (25 and 1/3 innings): Used the changeup 32.92% of the time and sported a 3.20 ERA in that span.

July (22 innings): Used the changeup 19.69% of the time and sported a 5.32 ERA in that span.

August (23 and 2/3 innings): Used the changeup 19.06% of the time and sported a 3.80 ERA in that span.

Fangraphs’ Eno Sarris wrote a good article the other day looking at which pitchers are throwing a higher percentage of changeups the last month, and added De La Rosa, who had the biggest drop in changeup percentage, to the conversation. We reached the same conclusion; RDLR performed better when throwing his changeup more often. However, he did not delve into its poor performance of late, and that’s just what I did here. Hopefully, you’ve learned a thing or two about De La Rosa’s changeup within both passages, and you’re no longer clung to the fallacy that it’s been effective all year.

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