Archive for Pitcher Aging Curves

At What Point Should We Worry About Velocity Loss?

I’ve written quite a bit this year on trends in pitcher aging, specifically velocity loss and gain. In the last iteration I focused on the odds of pitchers gaining velocity back after a season where their fastball dropped by at least 1 mph.

In that piece I listed a few pitchers to keep your eye on given that their velocity was down from 2011. In June, I wrote about CC Sabathia for ESPN and noted that the big lefty is likely beginning to “age”, as the odds are quite a bit higher that pitchers over the age of 30 do not gain their velocity back once they’ve lost it.

After thinking about it a while it occurred to me that there is of course the chance that these pitchers will gain their velocity back by the end of the year (as I noted in both pieces). We know that, generally speaking, pitchers gain velocity as the season goes on. Temperatures rise, and so too do fastball velocities. If this is the case I wondered at what point in the season we can say with greater certainty that a pitcher is throwing as hard as he is going to throw. Is there a particular month where a velocity decline is more likely to translate to or predict a full season velocity decline?
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Odds of Regaining Velocity, by Age

A number of pitchers with noticeably lower velocity this year either have landed on the disabled list or have had their seasons cut short due to injury. The Pirates’ Charlie Morton had Tommy John surgery (age 28, down 1.5 mph). The Tigers’ Doug Fister (age 28, down 1.1 mph) and the Blue Jays’ Brandon Morrow (age 27, down 1 mph) have both landed on the DL with oblique injuries. And the White Sox’ John Danks (age 27, down 1.5 mph) just started a stint on the DL due to elbow soreness.

Previously, I found that pitchers who lose at least 1 mph of velocity have over twice the odds of not throwing at least 40 innings in the subsequent year. This could simply be due to ineffectiveness, injury or both. A steep decline in velocity can create — or be a signal for — all sorts of problems. If a pitcher loses velocity simply due to a tired arm, they can increase their chance for injury by trying to pitch through it. Losing velocity also tends to make pitchers less effective over time. And once a pitcher loses velocity, the odds of regaining at least some of it the following year are very low (more on this below).

Today, I want to look at how age impacts the chances of regaining velocity for pitchers and then highlight some hurlers who fans should keep their eyes on this year and next year.

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How Secondary Pitch Usage Impacts Attrition


Last week I wrote about how losing velocity at different ages impacts a pitcher’s chance to throw 40 or fewer innings the next season (what I labeled “attrition”).

The overall finding was that losing velocity at any age increases the likelihood of attrition for pitchers, and that likelihood only increases with age. Overall, pitchers in the data set had a 29% chance of attrition between years one and two. If they lost at least 1 mph on their fastball, however, that rate jumped to 39%. Pitchers that didn’t lose at least 1 mph only had an 18% attrition rate–so half the odds. Starting at age 34, the attrition rate jumped to 50% and climbed for each age cohort until roughly age 39. (Thirty-eight-year-olds who lost velocity magically bucked the trend, attriting at about the same rate as all other pitchers.)

Eno Sarris asked me whether, as some have suggested, pitchers who relied on a change-up as their primary secondary pitch (such as a James Shields or Mark Buehrle) gained some kind of advantage, in terms of attrition. Do these pitchers have a lower chance of injury or ineffectiveness than someone who relies heavily on either a curveball (e.g. A.J. Burnett) or a slider (e.g. Ervin Santana)?

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Velocity Decline and Pitcher Attrition by Age

Note: The attrition data and chart was updated, showing a larger gap for just about all age cohorts

On May 26, the Twins released 33-year-old starter Jason Marquis. Considering how bad Twins pitchers have been this season, it really spoke to how bad Marquis’ numbers were to that point in the season.

In seven starts, Marquis posted a 8.47 ERA and a 7.25 FIP, numbers driven largely by a 7.5% strikeout rate, a 27.3% HR/FB and a sky-high .352 BABIP against. There was some speculation that, since Marquis has lost about 2 mph on his fastball since 2009, it was likely that he’d become more hittable — particularly at age 33.

This led to some discussion on Twitter about whether there was a greater likelihood that Marquis’ velocity drop at his age was more of an issue than if he had been a younger pitcher. It’s a legitimate question — whether diminished velocity has an impact, depending on age.

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Pitcher Aging Curves: Maintaining Velocity

Bill Petti published the first two parts of a series on pitcher aging. Bill’s first article focused on pitchers, in general, and the second was on the difference between starters and relievers. For the third installment, I’ll look at aging patterns for pitchers who maintain a relatively constant velocity from year-to-year.

From the previous articles, the average pitcher loses about 4 mph from their fastball from ages 21 to 38. In essence, most pitchers’ stats degrade as their fastball speed drops. Using the same methodology, I wanted to know how pitchers age when they don’t lose velocity on their pitches.

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Pitcher Aging Curves: Starters and Relievers

On Monday, Jeff Zimmerman and I launched our series of articles on pitcher aging. Readers should refer to introductory article, which includes general curves and a summary of the methodology. The general takeaway was that, as suspected, pitchers age differently than hitters. Generally, pitchers see their velocity peak in their early 20s and steadily decline by a full mile per hour by age 26. After that, velocity drops more sharply and continues a steep decline into a pitcher’s 30s.

Strikeout rates were tied to velocity, but not as closely after age 26. This indicates that those pitchers who survive into their late 20s and early 30s are less reliant on their velocity (and, most likely, their fastball) for strikeouts. A pitcher’s walk rate shows a some improvement through age 25 (due to starters), and then begins its decline.

In this article, I want to tease out some of the differences between starters and relievers.

Let’s quickly recap what the average aging curves look like for starters and relievers:

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Pitcher Aging Curves: Introduction

As on-field performance data has evolved, baseball enthusiasts have been spoiled with more precise measures of player performance. One area in particular is pitcher velocity. Whether through Baseball Info Solutions (BIS) or PITCHf/x, writers and researchers can now add a critical variable into their analysis that wasn’t readily available a decade ago.

Many readers of FanGraphs and Beyond the Box Score have seen Jeff Zimmerman’s position player aging curves. After reviewing them, I started to pester Jeff to see if he considered similar curves for pitchers — specifically in the area of fastball velocity. I was curious about the general pattern of decline for fastball speed and how it impacts overall pitcher performance. Luckily, Jeff already had been thinking about this.

Today, Jeff and I are launching a multi-part series on pitcher aging curves, which is centered on fastball velocity. This introductory article will lay out the methodology we used and — of course — the initial baseline curves for all pitchers, as well as starters versus relievers.

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