MLB Best Curveballs: The Best Curveballs of 2018

In today’s game where seemingly everyone throws hard, it takes more than just a good fastball to make the cut in the big leagues. These pitchers exemplify that and take it to the next level with the best curveballs of 2018.

On this week’s edition of the best pitches of 2018 we are going to take a look at the starting pitchers with the best curveballs in the game. As with the best four-seam fastballs piece from last week, we won’t simply be looking for the best individual curveball thrown but the larger body of work that the pitchers put together with the curve. We will still only be looking at starting pitchers with this exercise and to qualify, the pitcher must have thrown at least 250 curveballs on the season. These rankings are comprehensive based on several different aspects of the pitch. I won’t simply be ranking curveballs based on break, but also several other metrics deemed to be valuable to produce a productive curveball:

Movement

Movement is inherently one of the most important aspects of any pitch. This is especially true when discussing any type of breaking pitch. The point of the curveball is to confuse the batter by throwing something that moves very differently from the generic, straight fastball. Good horizontal and vertical movement are critical for having a good curveball but they are not the only factors that produce a quality bender.

Spin Rate

Spin rate is a newer concept at least to the general baseball audience, but it has been proven to be an important factor to pitch performance. A high-spin breaking ball will have harder and later movement than a pitch with lower spin. The later the ball begins to move the less time the hitter has to recognize the pitch and adjust, therefore having a curveball with a high spin rate will typically be more effective than a loopy curveball with less spin.

Whiff Rate

Swing and miss rate or “whiff rate” is the percentage of times that a batter swings at a pitch and misses. This is one of the single most important pitching statistics as it is a statistical illustration of how nasty the pitch is to the hitter. Ground balls are great but no damage can be done on a pitch that is never hit. Whiff rate is especially important when analyzing curveball quality as a curveball is often used as a strikeout pitch. It is thrown out of the zone to induce a chase.

xwOBA

Expected Weighted On Base Average for my money is the ultimate per plate appearance pitching stat. It takes into account strike outs, walks and balls in play based on their expected outcomes. Using expected outcomes is much better than actual outcomes because there are so many random and lucky things that can happen on a batted ball. Giving the pitcher credit for these events that are out of his control is simply the wrong way to look at it. Looking at xwOBA allowed by pitch type will give us an idea of how well the pitcher was able to produce the kinds of batted balls that typically result in outs.

Expected Weighted On Base Average as well as whiff rate are also good statistical illustrations of command. If the pitcher is able to execute and spot his pitches properly he is more likely to get swings and misses or induce weak contact. At this point there is not a great way to quantify command so this is as good a way as any to look at it.

Without further ado, I present the top curveballs by starting pitchers in 2018:

Jack Flaherty

Cardinals rookie Jack Flaherty ranks number five in this assessment. Flaherty had a coming out party in 2018 as he posted a 3.34 ERA, 3.86 FIP and a 2.3 fWAR in 151 major league innings, while striking out nearly 30% of the batters he faced. He even finished fifth in the National League Rookie of the Year Award race in a historically stacked field.

He had success this year relying mostly on his fastball but also with a good mix of sinkers, sliders and his curveball that worked as his out pitch.

His curve has above average horizontal and vertical movement, but it has below average spin. However, he did an exceptional job locating the pitch low and outside of the zone. This helped him produce an extraordinary 49% whiff rate on the pitch. The incredible lack of contact also led to his impressive .178 xwOBA on his curveball.

Flaherty only throws his curveball around 11% of the time but he gets such a high amount of swings and misses on the pitch that it is truly one of the most elite pitches in baseball. There has been a trend in baseball over the past few years of pitchers throwing more curveballs and perhaps this is a strategy that Flaherty could employ moving forward. This isn’t totally necessary as his other pitches are also really good, but it will be something to watch in the future.

Mike Fiers

Mike Fiers is an interesting name to see this high on the list. Most of the names on these best pitches lists have thus far been upper echelon starting pitchers and Mike Fiers certainly doesn’t belong in that category. Fiers would probably be best categorized as an average to slightly below average starting pitcher.

While he does provide some value as a starter, it was clearly not enough for the A’s, a pitching starved organization, to tender him a contract for the 2019 season. Fiers shouldn’t have much problem landing on his feet with some club but the extent of his next contract should be interesting.

Fiers lands on this list due in part to having a curveball with the most downward break of any curve in baseball. His curve also features a high spin rate which causes this downward break to be sharp and dive below hitters’ swings.

While he doesn’t generate a high number of whiffs with the pitch, he does keep the ball on the ground very well with his curveball. This limits the damage done on the pitch and contributes significantly to his .196 xwOBA allowed against his curve.

Mike Fiers is clearly not the sexiest name on the free agent market this off-season, but he is still a useful pitcher with a wicked curveball that should make solid contributions in 2019.

Nick Pivetta

Nick Pivetta may not be the most notable pitcher in the Phillies rotation, but he is certainly a pitcher with top shelf stuff. Pivetta may not even have the most famous curveball in his own rotation as everyone knows how filthy Aaron Nola‘s breaking ball can be. In fact, Nola was the first pitcher to not make this list.

Pivetta’s curveball fits the mold of a solid all-around good pitch. The pitch features solid movement both horizontally and vertically, the pitch features a high spin rate, and he got good results on the pitch in 2018.

Pivetta didn’t generate a ton of swings and misses with this pitch, matching Verlander’s 34% whiff rate, however, he did use his curveball more than most of the pitchers on this list. At 21.6% pitch usage, Pivetta nearly doubled Jack Flaherty’s amount of curveballs thrown.

This heavy usage of this solidly above average pitch makes the pitch play up in a way that isn’t captured in this methodology. While he didn’t have an xwOBA as low as some of the other pitchers already mentioned, he generated his .200 xwOBA more often.

Pivetta has been a useful yet volatile pitcher to this point in his young career, but if the Phillies are going to make some noise in the NL East in 2019, he will need to take the next step forward and show greater consistency from start to start.

Charlie Morton

The resurgent Charlie Morton takes the top spot on our best curveball list. There is an important thing to note about the top of this list before diving too deep into Morton himself. These pitches were ranked on a scale of 500 points with #2 Nick Pivetta and #6 Aaron Nola separated by only 13 points. Morton’s curveball outranked Pivetta’s by 29 points! By this method Morton had far and away the best curveball of 2018.

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His curve ranked near the top of just about every category. Morton’s mastery of the pitch starts with the movement. This pitch had more horizontal movement than any other curveball in the game while also having decent downward movement.

Morton’s curve featured one of the highest spin rates in the game making the movement play up as it was hard and sharp. Batters also showed us how dominant this pitch was by swinging and missing at 46% of the curveballs he threw and only producing a .199 xwOBA against. Morton was able to achieve all of this with the pitch while also throwing it a whopping 29.2% of the time.

There are a few factors that have led to Morton’s new found success as an Astro but his work with his curveball is certainly one of the big ones. Morton is one of the more intriguing free agent cases for the winter as he now has a two-year track record of being a top-end starting pitcher, however, he isn’t getting any younger and still carries with him a checkered injury history. One thing is for sure though, his curveball is among the game’s elite pitches.

That’s Call To The Pen’s look at the best curveballs in the game. Anyone you think was missing? Anyone too high? Comment below!