Unpacking Reynaldo López’s Good Start to 2021

Reynaldo López was simply not a good pitcher the last time White Sox fans saw him in the big leagues. He sported a 5.38 ERA in 2019 and a 6.49 ERA in 26 innings of work last year, and none of his peripheral stats indicated his poor performance was the result of bad luck. His FIP was right in line with his ERA, he was giving up high exit velocities on batted balls, his BB% and Whiff% were poor, the list goes on. With poor run prevention stats in the minors this season, it appeared that not much had changed for López this year, making it difficult to imagine he would stick on the major league roster.

However, during his brief stint in the bullpen this year, it is clear that he is a different pitcher than when he last appeared in a Sox uniform. López has made legitimate changes to his approach and mechanics that indicate his success out of the pen has some merit to it. While there are still areas for him to improve, and sample size luck may be boosting his performance to some degree, he has earned himself the chance to get a closer look moving forward.

First, the most apparent change in Reynaldo López’s approach has been a reliance on only his fastball and slider. The last time I looked at López in 2020, I recommended Reynaldo drop the changeup from his pitch mix due to the hard contact the pitch was prone to relative to his other pitches. The suggestion came with some risk, as López had a knack for swings and misses with the pitch, and it’s possible that hitters would fare better against his other pitches knowing the changeup wasn’t in the fold anymore.

Regardless, the White Sox seemingly agreed the trade off could be worth it, as López has practically removed the pitch from his arsenal. After throwing the pitch 15.6% of the time between 2018-2020, he has thrown it only 8 times this year out of 328 pitches.

His fastball usage has not dramatically changed, and the slider has essentially filled the changeup’s void. While it is worth mentioning that Reynaldo has faced worse competition this year compared to 2019 in terms of wOBA (by about .015), it is not sizable enough to account for the fact that López is seeing lows in expected SLG, wOBA, and HardHit% since the start of his White Sox career. Even though the sample size is still small, it seems likely that getting rid of his changeup has made a meaningful impact.

Still, the run values per 100 pitches on his fastball and slider in 2019 were both below average, his slider being in the 31st percentile among pitchers who had thrown more than 100 sliders. There was room for improvement on the two primary pitches he’s using, and he has made strides with both his fastball and slider.

The biggest change with López’s fastball has been his ability to locate it on the edge of the zone. While he’s throwing it slightly less in the zone as a whole, he has gone from throwing it on the ‘shadow’ (the edges of the zone) 50% of the time compared to 43.6% in 2019. He’s also avoiding pitches in the middle of the zone, throwing only 25.7% in the heart of the zone this year, down from 29.3% in 2019. Not only is he minimizing the hard hit balls he would get from leaving the pitch over the plate, but he’s also picking up more strikes on the pitch. Excluding balls in play, he has reduced the run value on the pitch from -1.2 per 100 in 2019 to -1.4 per 100 this year.

For his slider, López is locating it in the attack zones fairly similarly to 2019. However, he has added 2 MPH of velocity to the pitch since then, and the shape of the pitch has more horizontal movement. López was typically 2-3 inches below average with horizontal movement on the slider, but this year he has been an inch above average, with a spin rate 100 RPM faster than 2019 as well. The whiffs and ‘expected’ stats don’t jump out as being notably different since 2019, but this year’s iteration of the slider has been vastly better than 2020.

We may see these numbers take a different direction after a larger sample size, but even pitch statistics resembling something closer to 2019 wouldn’t be a letdown. At the very least, throwing the slider in place of the changeup has maintained the whiffs that made the offering valuable while reducing the loud contact his offspeed was prone to receiving. Alongside this, him locating his fastball better means hitters can’t just ignore that pitch either.

I also want to take note of López’s mechanics, because he has made clear adjustments since 2019 that may be a factor behind his success. López’s new arm slot was detailed in a post here last spring, and we can see that in his motion among other changes made to his delivery the last two years. Here is one clip from 2019.

And here is another from this year.

While I can’t claim to be an expert in pitching mechanics, it is clear that López has a much more balanced, controlled delivery. He is driving with his back leg more than simply leaning into it, which would generate more linear energy towards the plate. Here is a freezeframe of 2019 López on the left and 2021 López on the right at the same point in his delivery to illustrate what he’s doing differently.

In 2019, he appears much more off balanced as he starts his stride, and his torso is more open and angled upward, taking away momentum as he goes forward. This year, his upper and lower body are much calmer as he strides out, his torso is more neutral, and his shoulders are more level and on target. He is using his body more efficiently in driving to the plate, and getting into this more powerful position on each pitch could be the reason his slider velocity is up. While his average fastball velocity is about the same in previous seasons, he is hitting the mid 90’s more consistently than he has in the past, and this adjustment could help explain it.

López also made alterations by taking on a shorter arm slot, as demonstrated in the two images below from 2020 (on the left) and 2021 (on the right). This comparison shows he began making progress towards improving his back leg drive last year, but the most significant change over the last year has been with his throwing arm becoming more compact.

I’m not as convinced that this change has brought about the intended results. While he has located his fastball better, his release point has not been more consistent this year compared to last year, as the variance between his fastball release points have been slightly worse than 2020. One of the main reasons Giolito shortened his arm swing was to achieve a more repeatable delivery, but that doesn’t seem to be the case here in spite of the visual difference.

While Giolito’s release still varied more in 2019 than López’s did the last two seasons, we could see a drastic improvement the year he compacted his arm arc, whereas with López we don’t. It is possible that there is another purpose behind the shorter arm swing, and López’s statistical improvements in commanding the corners and limiting walks show things seem to be working for him so far. Still, it may be worth keeping tabs on if he can maintain these gains, or if he makes further adjustments to his mechanics. Beyond questioning the relationship between his new delivery and the results, another area of concern with his new delivery is the direction of his shoulders as his foot plants.

He seems to be getting less separation between his lower body and upper body than in previous seasons, which may be holding back some of his max effort throws (he hasn’t hit 99 MPH yet this season). We can already see his left arm is visible on the left side before his hips have really opened up towards the plate, which looks like his upper body may be firing a bit too early in the sequence. For comparison’s sake, we can see that López’s lower half is less rotated than Lucas Giolito and Lance Lynn at the point when their left arms come across their body.

While he certainly isn’t perfect, López has made positive changes to his gameplan and mechanics on the mound, and makes him worth keeping an eye on down the stretch. He may not find a spot in the Sox rotation (assuming all remain healthy), López could be an extremely valuable arm out of the bullpen down the stretch.

(Photo by Kamil Krzaczynski-USA TODAY Sports)

Take a second to support Sox Machine on Patreon
Articles: 3
Newest Most Voted
Inline Feedbacks
View all comments

This is a fantastic breakdown, Edward. You say you’re not an expert in pitching mechanics, but your breakdown of his changes to his throwing motion was incredibly well done!

Any idea if perhaps he was working out of the windup instead of the stretch in the 2019 picture as well when you did the side-by-side comparison of how he’s driving off his back foot now and staying more in line to the plate? The windup has an innate rocking motion that might have been compounding the problem as well if that’s the case.

Hope to read more of your work, excellent job!


I’d like some more, please.