The Making of a Reliever - Middle, Late, and Closers

A more technical look into what makes a successful middle reliever and late reliever/closer.

When I tell you to imagine the bullpen, you probably think of the collection of 10 or so guys that come on to pitch whenever the starter is done for the day. What if I told you this bullpen consists of two very distinct groups of pitchers? While everyone in the bullpen is a relief pitcher, they are either considered a middle reliever or a late-inning reliever/closer.

In this article, I’ve taken eight of the Guardians’ relief pitchers and split them into two groups of four. Four middle relievers and four late-inning relievers/closers. The purpose of this is to show just how different these two groups of pitchers are and what makes each group successful. I’ll take a dive into the pitchers’ velocities, locations, pitch arsenals, and leverage situations and discuss how each of these factors makes them successful.

The first factor is perhaps the most important and certainly the most scrutinized by the media and fans — velocity. As soon as a pitcher’s velocity drops even the slightest amount, people begin clamoring about an injury or saying he’s “washed”. While velocity is certainly important, the definition of a “good” velocity varies for each pitcher. Below is a simple chart of four middle relievers, four late-inning relievers/closers, and their average velocities so far in 2024.

(All stats are as of June 13, 2024.)

As you can see above, the late-inning guys throw almost two miles per hour faster than the middle relievers. However, this doesn’t mean that they’re automatically better pitchers just because they throw harder. A high velocity is usually a good sign of success for pitchers. That’s why the high schooler who can throw 90 miles per hour will be drafted a few rounds before one who throws 82. If you dig just a bit deeper, though, you’ll see that a pitcher needs more than just speed to be successful. He needs to be accurate.

Obviously, the goal isn’t to throw every single pitch in the middle of the strike zone. If that were the case, we’d see a lot more home runs. However, an elite pitcher should be able to throw the ball to a desired spot each time. Whether that’s a sinker a foot outside of the zone that tricks the hitter into swinging or a fastball that lands perfectly in the middle of the zone and catches him looking, a pitcher who can locate his pitches can be extremely successful.

Below is a chart of the same eight pitchers and their zone% so far this year. This stat measures exactly what you probably think. The percentage of time that a pitcher throws a pitch into the strike zone. Now, as mentioned earlier, a pitcher isn’t always aiming for the strike zone. However, the more looking strikes he can get in the zone, the less he has to worry about walking hitters. So this is the stat we will use for accuracy.

We can see here that the late-inning relievers throw pitches in the strike zone just over 4% more often than the middle relievers. The heavy lifting here is done mostly by Gaddis and Smith who are throwing 4.6% and 6.3% more accurately than the league average. For the middle relievers, it’s only Hentges who is throwing more accurately than the average 50.1%.

This accuracy is largely dependent on the type of pitch thrown. It’s going to be more difficult for a pitcher to throw a sinker in the zone than it is a fastball. Let’s next take a look into the types of pitches that Cleveland’s relievers are throwing and the value of each pitch type. To illustrate this value, I’ll be comparing the pitchers’ Stuff+ for their arsenals as a whole. This stat looks at the pitcher’s release point, velocity, vertical and horizontal movement, and spin rate (via Owen McGrattan, fangraphs.com) with 100 being the league average.

Sometimes a wider arsenal makes a pitcher better. However, this is only in certain cases as shown above. Here, we see that the middle relievers have wider pitch arsenals overall, but their average Stuff+ is lower than the late relievers who employ fewer pitch types. This can be for any number of reasons, but the most likely one goes back to zone%. While the middle relievers have more pitch types they can throw, they most likely do not have great command of all of them.

As an example, let’s compare the Baseball Savant charts for Nick Sandlin and Hunter Gaddis. Sandlin’s slider is shown on the left and covers a lot more ground around the plate than Gaddis’ on the right. So even though Sandlin has a wider arsenal and throws four different pitches versus Gaddis’ three, Gaddis’ is valued 21 points higher because of his ability to keep it in — or close to — the strike zone.

The final factor we’ll look into for this bullpen is the situations that they are used in. Some pitchers are able to thrive when the lights are the brightest and the stress is higher while others crumble under the pressure. To put this into numbers, I’ve compared the pitchers’ leverage indexes with their ERAs and the percentage of inherited runners that they’ve allowed to score (IR-A%). An LI of 1.0 is a neutral situation so the higher the number is above 1, the more stressful the situation is (i.e. entering the game with the bases loaded in the bottom of the ninth will be way over 1).

Taking LI out of the equation, it looks like the middle relievers are pitching better. While that is true, it is extremely important to read these numbers in the context of their LI. The middle relievers are pitching in less-stressful-than-normal situations while the late-inning relievers are pitching in more-stressful-than-normal situations. It should also be noted that Avila’s ERA and IR-A% are inflating the average since they are so much higher than the others.

My initial thought after putting this chart together was that each pitcher had been placed in the correct role for this team based on the results they'd seen. Since each pitcher had a low ERA and IR-A% at their respective LIs, I’d assumed the LI was the reason. However, it’s clear to see that we do not have enough information to make this assumption as we have nothing to compare it to. As an example, Herrin has only pitched in the ninth inning twice this year — and never in extra innings — so we don’t really know how he performs under pressure. However, as pitchers like Herrin and Hentges continue to excel in low-mid leverage situations, they will likely see their opportunities in high leverage situations increase (especially Hentges, who has been used as a high leverage arm in the past).

One final chart shows the overall success rate of all eight pitchers via their Fielding-Independent-Pitching — a number that quantifies ERA, strikeouts, walks, hit-by-pitches, and home runs into one number — and their expected weighted On-Base-Average against - hitters’ exit velocity, launch angle, and sprint speed (aka their success rate) against these pitchers (via MLB.com). Lower numbers are better in both stats for pitchers (hitters want high xwOBAs).

Taking all of these charts into consideration we can see what separates Cleveland’s great middle relievers from their elite late inning guys. Some of them, like Morgan, were starters at the beginning of their Major League careers, but found themselves better suited for relief roles. While there’s not a singular thing that makes a pitcher fit this role, it’s clear to see what they are made of.

Their pitches run just a few miles per hour slower than the closers and even the starters. On the other hand, they have wider pitch arsenals than the closers which can be a huge advantage. Since they often see more innings of work than a one-inning specialist like Clase, they’re able to show off multiple pitch types to the two or three innings worth of hitters they face to keep them on their toes.

All in all, these numbers just continue to prove how successful this bullpen has been as a whole this season. However, it also shows that the late-inning relievers have found more success. We’re just lucky enough that the middle relievers have also been successful and have been overshadowed by the top-of-the-league back end. In a year where nobody expected them to be this good, they’re proving everyone wrong.