Let’s re-visit Brad Peacock’s slider

On Wednesday, against the Baltimore Orioles, Brad Peacock finished off the game with three strong innings, giving up two hits while striking out five. Of course in a one run game, Hinch was always going to be questioned for leaving Peacock in to finish the game over the arguably effective closer, Ken Giles. But what did Hinch see in Peacock to leave him out there for the last inning?

To start off, Peacock threw 39 pitches with 25 of them being sliders, showing immense trust in the pitch. This is just par for the course for Astros’ pitchers, but he got an outlandish 9 whiffs on the 25 sliders. One of the main comments thrown around the Slack channel was that his slider had incredible movement.

Perhaps unsurprisingly, this holds true in the numbers as his slider had an incredible 13.5 inches of horizontal movement. For a comparison, looking at 706 other sliders, Peacock’s horizontal movement on Wednesday had a Z Score of 4.27. A Z Score, in simple terms, is the number of standard deviations above or below the average. So in other words, Peacock’s horizontal movement was 4.27 standard deviations above the average. While this does not necessarily make it a great pitch, it is still remarkable.

So now the question becomes, did Peacock’s slider become even better this year, or was it just “on”? Well, it’s impossible to answer the question based off a one game sample, but it did lead to an investigation of his 2017 slider compared to his slider in this game. Below, you can see a chart showing Peacock’s horizontal movement on his slider over 2017.


What already stands out is that Peacock never averaged over ten inches of horizontal movement in any game last season. One could argue that he threw some with a lot of horizontal movement and others with more vertical movement, so average is not a great comparison. While that’s probably true, the max horizontal movement Peacock had on any slider in 2017 was twelve inches. The fact that he averaged more horizontal movement in this game than he got on any single pitch in 2017 makes this intriguing. It also must be pointed out that he threw a slider with 17.5 inches (literally the width of home plate) of horizontal movement. That is insane! To put this wordy paragraph into a picture, see below and notice the outlier on the far right from Wednesday. Of note, is that the error bars are the min/max horizontal movement on his sliders per game in 2017 and 2018.


One thing to notice is that in his first couple of outings in 2018, the slider Peacock threw was not vastly different than last year’s pitch. So what happened? It’s really impossible to know considering this is just one game, but it is something to watch moving forward. It could just be a new variation of the pitch he worked on in Spring Training, but since Spring Training numbers are horrible, it is hard to find out if that’s true or not. Either way, this was a pitch not seen in 2017.

It would be odd to say that Peacock has a “new and improved” slider considering the pitch was phenomenal last year, but it can be said that on Wednesday it was different. It was different than at any other point last year. Maybe Peacock will go back to the slider he threw in 2017 like he did in his first couple outings of the year, or maybe Peacock has developed a new slider. Whatever the case may be, Peacock’s 13 inches of movement on his slider made the pitch unhittable. I can’t help but feel sorry for hitters if he starts to mix that pitch in more often with the rest of his repertoire.

All data is sourced from Brooks Baseball

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