Where It All Started
The year is 2018. Edwin Diaz, nicknamed Sugar, was as dominant as a relief pitcher could be. He led the MLB in converting 57 saves for the Seattle Mariners. Sugar had ridiculous numbers such as his 1.96 ERA, 1.61 FIP, 15.22 K/9 and worth 3.5 fWAR. That was good enough for Brodie Van Wagenen to pull the trigger and acquire Diaz. Brodie had to give up prospects Jarred Kelenic and Justin Dunn. BVW also had to take on Cano’s hefty contract. Giving up a top prospect for a closer is risky since RP are versatile. Diaz had to at least be a reliable, consistent closer. Looking at 2018 and his overall career to date, it was almost certain he would. Then 2019 came along, and long story short, Sugar did not perform well in the Big Apple.
We all know that Edwin Diaz was miserable in 2019. It’s obvious even to people that don’t know baseball. It’s almost unimaginable how big of a difference 2018 Diaz was from 2019. Now we must find the answer as to why he underperformed so dramatically. The chart below displays statistics from FanGraphs and Baseball Savant that I put together and will reference to throughout the article.
Diaz’s Electric Arm
Let’s start with Diaz’s arm, under ‘Pitch Info’ in my chart. It wasn’t a matter of being fatigue after throwing 73.1 innings in 2018. He isn’t old either, so it’s not age as Diaz is 25 years old and just now hitting his prime years. To prove it wasn’t arm fatigue — or any sort of right elbow bone spur issues — we look at his pitch velocity. His average fastball velocity in 2018 was 97.3 mph compared to 97.5 mph in 2019. He threw his slider a tad faster too on average, jumping from 89.1 mph to 89.5 mph. He has an extremely explosive arm. So, velocity decline and/or arm fatigue wasn’t the issue.
Hard Hits = Hard Times For Sugar
When comparing 2018 to 2019, Diaz got hit noticeably harder. This was one of the major issues with his horrid season. Take a look at the ‘Stat Cast’ numbers in the chart. Hitters barreled the ball 6.3% more often this year. The average exit velocity jumped 1.9 mph, and Diaz’s hard-hit rate jumped up from 35.3% to 45.3%, a 10% difference. This is massive as a 45.3% hard hit rate is within the bottom 2% of the league. That means Diaz was one of the worst pitchers when it came to preventing hard hits/contact. To give you perspective, Stat Cast labels a hard hit as being 95+ mph. That means 45.3% of all hits against Diaz were at least 95+ mph; not good. To go along with these numbers his xSLG, expected slugging, increased .110 points. An xSLG of .351 is respectable but is the worst mark of Diaz’s career.
The Art In Pitch Value
Diaz’s pVAL, found under ‘Pitch Info.’, easily stand out when comparing his two most recent years. His fastball pVAL decreased from 13.8 to -0.7 and his slider pVAL fell from 9.4 to -2.9. pVAL indicates the number of expected runs saved/ run expectancy by adding up every single pitch thrown, of that pitch type, over the course of the season. Diaz’s 2018 fastball had a run expectancy of 13.8 runs, which is solid. This number is really -13.8 runs expected, but FanGraphs flipped the number, so a higher positive number is better. Diaz’s 2019 fastball pVAL of -0.7, which means that 0.7 runs were expected off it, isn’t so good. Both of his pitches weren’t preventing runs as they totaled -3.6 pVAL. The same two pitches had a 23.2 combined pVAL in 2018, meaning 23.2 runs were expected to be saved. That’s a massive difference from year to year.
Diaz’s fastball from year to year actually looked to be better in 2019. Look at the ‘Pitch Tracking’ section in the chart for the comparison. His xBA, spin rate, K%, Whiff%, and PutAway% on his fastball all had better marks in 2019. He had 71 strikeouts with the pitch, compared to 48 in 2018. This is because Diaz used his fastball 3.4% more often this past year and because he couldn’t rely so much on his slider; I will get into his slider shortly. The bad part is that Sugar’s SLG against his fastball skyrocketed from .250 in 2018 to .436 in 2019, along with his xSLG from .294 to .326. This is due to Diaz getting torched for 9 home runs off the pitch, while hitters only hit 2 home runs off his fastball in 2018.
It’s interesting that his xSLG didn’t rise nearly as much as his SLG. This suggests that what was expected didn’t happen, meaning that his fastball let up more damage than it should have. Diaz’s fastball looked solid when it came to getting k’s, but he gave up the long ball and hard contact nonetheless. That is why is fastball pVAL was -0.7. He did have strikeout success with his fastball, but the pVAL on the pitch wasn’t good since he gave up home runs far too often, making for a negative run expectancy on the pitch. Even though his K%, Whiff%, and PutAway% increased, when his fastball was hit, it was hit for damage.
Diaz’s slider was not good, to say the least. Again, looking at the ‘Pitch Tracking’ on the chart, comparing the pitch from year to year is as if a totally different pitcher threw the ball in 2019. His xBA and xSLG numbers rose dramatically, while is K%, Whiff% and PutAway% all declined quite a bit. 3 home runs were hit off the pitch in 132 AB in 2018, and 6 home runs were hit off the slider in just 74 AB in 2019. Hitters were on his slider. That is why Diaz threw his fastball a tad more, and found more strikeout success with it, but still let up the long ball on each of the two pitches.
Now we look at why Diaz’s slider was an issue. One reason as to why Diaz’s slider was not effective is because of the movement he got on the pitch, or lack thereof. He had -0.7 inches of vertical movement when compared to the average slider within +/- 2 mph, +/- 0.5 feet of extension and release and -1.1 inches of horizontal movement compared to the average slider using the same criteria. Having a negative number here means less movement compared to pitchers who threw a similar slider within the above criteria (this is the criteria that Baseball Savant Uses). Obviously, the more movement the better. Diaz’s slider stayed flat and didn’t have good bite to it, which lead to hard hits.
Location, Location, Location
Diaz’s slider location was another issue. The picture below shows sliders thrown in the heart of the plate with two strikes. Look at the red heat map low and in the middle of the zone. That’s a solid number of sliders over the heart of the plate with two strikes. We can take this with a grain of salt as some of these offerings came on 3-2 counts. Either way, that is a pretty decent amount of sliders in a 2-strike count down the plate. His slider should start off as a strike and move out of the zone, but since Diaz’s slider didn’t have good movement, both of these issues mix with each other in a way.
The next picture displays sliders out of the strike zone. There are only three occurrences where a slider outside of the zone turned into a base hit. The non-highlighted dots show the location of all sliders outside of the zone that were not hits. Diaz’s success with his slider occurred when he threw it off the plate, albeit pitches not swung at were balls, and 3 ball counts turned to walks.
The picture below presents sliders hit within the zone. Too often a slider ended up in the middle part of the zone. The red heat map shows this. Diaz’s ‘mistake’ pitches were more vulnerable to be hit. When Diaz located his slider off the plate and got hitters to chase, he found success. But, leaving a slider that doesn’t have much movement in the middle of the zone is a recipe for disaster.
Mets Defense and BABIP
Edwin Diaz’s combination of giving up hard contact, a fastball that generated strikeouts but was hit hard and an ineffective slider, are the culprits to a subpar 2019 season. However, there is another aspect I want to look at; the Mets defense along with the rise in Diaz’s BABIP. New York’s defense ranked last in MLB with a -91 Rdrs (defensive runs saved above average). For a team built around pitching, fielding this poorly surely doesn’t help.
A bad defense could be part of the reason as to why Diaz’s BABIP jumped from .281 in 2018, to .377 in 2019. However, higher BABIP can be due to Sugar’s hard-hit rate and exit velocity numbers rising as well. Harder hit balls have a greater chance of falling in for a hit. Another reason that Diaz’s BABIP rose is because his GB% decreased. He induced ground balls at a 44.4% clip in 2018 but declined to 36.7% in 2019. In turn, this made his fly ball% rise 8.5%. That means hitters were getting the ball in the air more often which can point to more balls dropping in for hits rather than ground outs. The horrid defense throughout the year most definitely didn’t help Diaz. Where they aren’t at fault is the 15 HR that Sugar surrendered.
Light At The End of The Tunnel
There are three bright spots when looking at Edwin Diaz’s body of work this season. First is his strikeout ability. Even with a slider that had little movement, Diaz struck out 39.0% of batters faced, to the tune of a 15.36 K/9. The 39% strikeout rate is within the 99th percentile of all pitchers. That’s fantastic.
The second positive for Diaz was his 3.07 xFIP. This is evident when comparing that number to his 5.59 ERA and 4.51 FIP. Sugar’s xFIP looks solid, even though he had such a down year, because this stat uses projected home run rate, not actual home runs given up. It adjusts for how many home runs should have occurred based on the amount of fly balls that pitcher gave up. It basically acts as a predictor of what should have occurred. Diaz’s 26.8% HR/FB rate was absolutely ridiculous; he had a 10.6% HR/FB in 2018. That number pretty much means every fourth fly ball left the park. That rate was the third worst in the entire league among all qualified SP and RP. This correlates with Diaz’s 2.33 HR/9, which was the worst among all qualified SP and RP.
The bloated home run rates based off the amount of fly balls given up is why his xFIP is a respectable 3.07. Other factors to Sugar’s xFIP, and FIP, being lower than his ERA is that these two stats take into account home runs, strikeouts and walks, the latter two of which he had solid ratios. Having a lower xFIP when compared to ERA and FIP point to a pitcher that was dealing with some bad luck, and better days ahead.
The third bright spot for Diaz was his excellent 2.63 SIERA. On FanGraphs, the scale shows that a 2.90 or lower SIERA is defined as being excellent. SIERA considers strikeouts, walks, balls in play and is ballpark adjusted. Diaz generated plenty of strikeouts, a respectable walk rate, and got unlucky with fly balls in play turning into home runs 26.8% of the time. That is why his SIERA looks good. But the final results weren’t so pretty due to increase in hard contact against and some luck going the hitter’s way. Overall, Diaz’s strikeout ability, 3.07 xFIP, and 2.63 SIERA point to a pitcher that was dealing with bad luck when it came to expected home runs, versus actual home runs.
In Summary …
Edwin Diaz’s 2019 season on the surface was a dumpster fire. A 5.59 ERA, 1.38 WHIP, 0.0 fWAR, -0.6 bWAR, 7 blown saves and a 2-7 record will surely do that. The main culprits were his flat, poorly located slider and too much hard contact that turned into 15 balls leaving the park. However, his bloated HR/FB%, strikeout ability, xFIP, and SIERA show that he was dealing with some bad luck. These numbers point toward an expected solid pitching performance this past season, yet Met fans had to endure a closer that made them sick. Here’s to hoping these expected stats come to fruition in 2020.
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