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Which Pirates Starter Was the Most Durable in 2018?

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MLB: Kansas City Royals at Pittsburgh Pirates Charles LeClaire-USA TODAY Sports

Which Pittsburgh Pirates starting pitcher was most durable in 2018?

An interesting opinion from Brian Kenny during the World Series sparked this post.

I unfortunately must paraphase, as the exact quote seems to have never made it to the internet in any printable or embeddable fashion. Here it is:

“Removing Rich Hill was a no-brainer. He was gassed. The spin rate on the curveball was way down, as was his velocity.”

If anyone can find the exact quote please let me know!

After hearing that from Kenny, I wondered out loud who the most durable Pittsburgh Pirates starting pitcher might be. We used to be able to simply ask: Who pitched the most innings? Yet as the game has evolved, that metric isn’t nearly as sturdy as it used to be.

Following Kenny’s lead, what if we looked at in game changes, inning by inning, for spin rate on breaking balls and velo on fastballs?

Breaking Ball Stamina

This is the part where I tell you this is not a perfect study. In fact, it’s pretty far from it. So, let’s consider this entire post as a starting point.

Spin means different things for different pitchers. One man’s slider might benefit from lower spin while another’s might feel higher spin to be necessary to be effective. It makes for an entirely messy study, but ah hell let’s give it a try anyway.

Tap/click to enlarge

Here we see the five Pittsburgh Pirates starters likely to begin 2019 in the starting rotation. We also see their 2018 average spin rate on all breaking balls by inning, as well as their average season spin rate overall. For comparison’s sake, we include the league-wide figures as well.

Here, an asterisk indicates a sample size of less than 15 pitches. Three dashes (—-) indicate that no breaking balls were thrown by that pitcher in that inning. All figures are as per Statcast.

Now that the fine print is out of the way, let’s dive into this. I have illustrated the change in average spin for each inning relative to that pitcher’s season-long average spin rate. Results are curiously mixed. Jameson Taillon, for example, seems to fluctuate the most — positively and negatively — including a rather large swing in the eighth inning. Chris Archer, who lives and dies by the breaking ball, starts off with lower spin but progressively meets or exceeds his usual spin until the sixth inning.

All of these starters seem to start off with lower spin rates, in particular Joe Musgrove. In all reality, there is not much to make of that. A bit of context helps. During my time covering minor league baseball for the Pirates’ organization and others, I have repeatedly heard that during the first few innings of any particular start, pitchers are attempting to “get their feel” for how their breaking stuff (and location for that matter) on that particular day. I would often hear an accompanying statement: “The better ones find that feel much more quickly.”

Looking at this chart with that context, the figures make sense. It also opens the door to the possibility that perhaps we should not be looking at maintaining spin rate as a measure of duability, but rather an ability to maintain feel and consistency. This might result in a raised eyebrow at least when considering Taillon’s drop in the 8th inning with a decent sample size.

We can draw some other educated guesses out of this as well. Was Trevor Williams as effective as he was in the season’s second half because he maintained his spin rate on breaking balls (even though he used them far less than fastballs)? Does Archer suddenly lose feel in the sixth inning? All interesting questions for another time, but let’s move on to something much more measurable.

Fastball Stamina

Tap/click to enlarge

Ah, good old velocity. Measurable. Real. Easily digestible.

This chart is setup the exact same way was the spin rate chart, only with average velocity as the criterion. Once again, all data as per Statcast.

A quick glance shows no significant drops for Pittsburgh Pirates starters. In fact, no starter lost more than a mile per hour off of their fastball as they work their way through a game.

Unfortunately, the league figures here do not tell us all that much, as the sample size is large enough to establish a solid degree of reliability.

Perhaps the best conclusion we can draw from this is just how much a particular pitcher can lose from his first offerings to his final ones. If we look at it this way, Musgrove might be the poster child for durability, at least in terms of velocity. His rate of change stays more or less consistent from the fourth inning onward, and he even enjoys a slight uptick if he dials something up for the eighth inning.

Much like spin rate, we might need to refine the angle at which we are looking at this. With velo, it is inevitable that most starting pitchers will lose a little bit the further they go into games. By most accounts, Pittsburgh Pirates starters seem to not lose all that much. More study would be needed to fully quantify that — for example, we might want to compare them against other clubs — but this is a good starting point nonetheless.