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[Joe]

FiveThirtyEight | Baseball's ‘Hot Hand' Is Real
After analyzing MLB's fastballs, we found that every pitcher has both an ace and a bum lurking inside them.

Sabermetricians usually insist that such streaky performances are really just an artifact of fans and journalists forcing narratives onto random patterns. No matter how much it seems like a pitcher is getting hot, the more likely explanation is that they just happen to have bunched a few good innings together. But that's not quite correct: Using a new method that focuses on fastball velocity, we found a way to detect whether a pitcher is actually throwing with a hot hand

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Methodology

First, we focused on each thrower's hardest types of fastball, which avoids situations where pitchers were intentionally varying speeds, such as between two-seam and four-seam heaters.

We then run a generalized linear model that predicts a pitch's velocity based on who's pitching and the number of pitches they've thrown.

Then variables that can affect pitch velocity are controlled for such as: the effects of each stadium, stadium elevation, game-time temperature, pitcher fatigue during the game, baserunners, and game score.

Then we apply a 'Hidden Markov Model' to the residuals of the second model, searching for two hidden states — corresponding to hot and cold — within each pitcher.

Once we've done all that, we can go through a year's worth of fastball velocity readings and determine when a starting pitcher is hot or cold.

Result

We found that the typical pitcher goes through 57 streaks in a season, jumping between hot and cold every 24 pitches. And not only did we find streaks, but we also found that the difference between being in the freezer and on fire is huge: The average pitcher moves up or down by an average of about two miles per hour when shifting between states.

Every starting pitcher in our data shows a noticeable pattern of switching between hot and cold states.

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Our approach isn't just backwards-looking, either — we can also predict whether a pitcher will be hot or cold in the future. Using just the first two months' worth of 2016 data, we tried to predict every pitcher's subsequent fastball velocity. Our model was able to predict how hard the next pitch would be better than a guess based on the pitcher's season-long average would be able to, suggesting that it's able to pick up on when a pitcher is hot or cold at any point in the season after June 1.

The predictions don't just affect fastball velocity. The hotter a pitcher was projected to be on a given pitch, the greater the probability was that the next fastball would yield a swinging strike, even accounting for the increased speed of that heater. Similarly, a pitch was significantly less likely to go for a hit, and less likely to yield extra bases, if a pitcher was considered hot.

Although our approach can tell us when pitchers are on or off, it can't tell us why.

If hot streaks are real, as our results suggest, they probably apply to more than just pitchers. We started out looking at fastball velocity because it is one of the most consistent and important performance characteristics in baseball, but our method could be applied to anything, from how hard a batter is hitting the ball to how often he swings the bat.

As evidence mounts that player performances do vary from hot to cold, it's probably time to revisit the long-held sabermetric belief that such streaks are a fallacy. Whether a player is in the zone or in a funk, it's not just magical thinking — it actually tells us something real about how he will play in the near future.

 

[Saganator]

This is really fascinating. My mind is going nuts thinking about how to use this data, especially when they get data on hitters. That's one reason, of many reasons, why I love baseball. The stats and data, I used to spend hours looking baseball player and team stats when I was kid.

It would be interesting to see this data alongside the Indians winning streak.

This thread deserves a bump!