Luis Severino has had a tale of two halves, with the second half being far below the expectations he set before the All-Star Break. Some have posited that Severino is tipping his pitches. There is also the possibility that Severino is slowing down because he has never reached 200 innings professionally. Neither of those will be the focus of this article, though maybe in the future it would be worth looking at Severino’s delivery in the first and second halves.
This article is going to focus on two of his pitches: the slider and the four-seam fastball. The first question would be the stuff itself. Has it regressed in terms of velocity or control?
In the case of the slider, this chart from Brooks Baseball shows the horizontal movement and vertical movement of all Severino’s pitches. A quick note: the closer to zero on both the X and Y-axis, the less movement horizontally/vertically there is. Further from zero means more movement:
The fastball movement is about the same, but the focus, for now, should be on the slider. Those dots closer to the zero are from the most recent months. Meaning, there has been less vertical and horizontal movement in his slider since the start of the season. In the case of horizontal movement, it’s only about an inch, but the vertical movement is closer to three or four-inch difference.
Has this led to any change in the performance of his slider? Not really. He did give up four home runs in July versus two in the first half altogether, but his K% and BB% with the pitch stayed consistent, as did the Whiff% (amount of swings and misses the pitch generates).
There is no straightforward explanation for the dip in slider usage over time without being in the clubhouse or watching the bullpens. However, it seems important to note when considering Severino’s four-seam fastball usage has increased.
The below chart shows the slugging percentage against each of his pitches. The black line shows his four-seam fastball. Since the beginning of June, opponents have been slugging better than .500 against his fastball, with a peak in the .700 range in August. Yet, Severino has double downed on using the fastball.
July was a bad month for all Severino’s offerings, but one thing that has stayed consistent in August is that opponents are slugging greater than .600 against his fastball. With that, Severino is getting fewer whiffs per swing on his fastball in the second half, shown below:
So, there’s a reason for this, right? As mentioned earlier, tipping pitches will not be touched on here, nor will the possibility of injury, but there was something interesting in this next chart. It covers the vertical release point of Severino’s fastball, put more simply, how high is his hand when he releases his pitches.
Now, all his pitches have increased in vertical release point, but none have suffered as much as his fastball has in terms of performance. Is this typical of Severino? Does he always increase the vertical release point over time? Well, no. But, the only other time Severino had a higher release point was during his 2016 campaign, when he posted a 5.83 ERA. That looks like a pretty consistent relationship.
There is no solid explanation as to why the increase in vertical release point would lead to poor performance. The only speculation could be that hitters are seeing it better out of his hands, especially since there is not too much movement to his four-seamer.
Now, going by his FIP in the first half, Severino overperformed by close to .5 ERA points. That can be explained by an extremely low HR/FB rate, which Severino has never been known for. He posted a HR/FB% around 6% for the first three months while he has posted a 20.5% HR/FB% in the second half.
That brings his overall season HR/FB% to 12%, much closer to his career average of 14%. It seems like Severino’s true homerun prevention talent lies somewhere between the 6% and 20% range, rather than sitting at either end of the spectrum.
To go along with this, Severino has seen his groundball rate drop 11 percentage points from 43.9% to 32.1%, while his line drive rate has jumped from 22.4% to 33%. That is going to contribute to more hits, as demonstrated by his .400 BABIP in the second half versus his .278 BABIP before the all-star break. His career average sits closer to .290, so again somewhere closer to that .278 he posted earlier this year.
All these regressions since the all-star break come back to that increase in his vertical release point of his fastball, which has led to a higher slugging percentage against the pitch and more home runs overall. That is reminiscent of his worst year as a professional in 2016. This really feels like a mechanical change, either knowingly or unknowingly, that has gone extremely wrong.
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