When Good Stuff Goes Bad

While 2017 was the year of the dinger, it also looks like it was the year of velocity. Has baseball changed (both the sport, and the physical ball itself)? The signs point to yes – but on the pitching from, the importance of velocity has never been higher. Exhibit A:

That’s not average. That’s not maximum. That’s … the slowest. Let’s borrow a little bit of math from the documentary “Fastball” to just put into context how crazy this is.

The league average four seam fastball velocity in 2017 was 93.19 mph. That represents a velocity of 136.68 feet per second. This pitch would reach home plate from the typical release position of 55 feet in 402.4 ms. Given an average of 2 synapses forming in the brain every second, there would be approximately 201.2 synapses formed between the time a ball leaves the pitcher’s hand and the time it reaches the plate. Compare this to 96 mph – which represents a speed of 140.8 feet per second, and reaches home plate in 390.6 ms. That difference of 10.2 ms represents the opportunity for nearly 6 more synaptic connections to form in the brain. Of course, these numbers represent the time and synaptic connections required to just watch a screaming fastball fly across the plate – it doesn’t factor in reaction time, or the time to actually swing the bat. Baseball is hard.

With all of that in mind – shouldn’t the 96 mph heat just blow away every hitter? Should guys like Marco Estrada and Dallas Keuchel even bother going out on the mound? Why isn’t Joe Kelly the greatest pitcher to ever throw a baseball? How did Rajai Davis hit a grand slam off Arolids Chapman in last year’s World Series (no one will ever know the answer to that, and if they claim they do, they’re a giant liar).

On occasion, good Stuff can go bad. Using the Stuff metric, and BP’s command, and control statistics – let’s find out what trends in the data can be velocity’s kryptonite.

A quick refresher – Stuff is a measure of movement, change in velocity, and peak velocity. It also factors in pitch usage, and breaking pitch (curveball and slider) velocity. The metric has proven to be tightly correlated with strikeouts per 9, ERA, and FIP. For the sake of this evaluation, i just looked at K9.

How many pitchers had great stuff and great k9 (in the upper third of all pitchers who threw more than 50 innings in 2017)?

Great Stuff vs K9 results
Poor K/9 OK K/9 Great K/9
Poor Stuff 64 53 32
OK Stuff 54 49 50
Great Stuff 31 51 67
Minimum 30 innings pitched in 2017, total 451 pitchers

That’s not too surprising. The pitchers with the highest K9 also had the best Stuff (67 pitchers met this criteria. The pitchers with the worst Stuff had the lowest K/9 (64 pitchers met this criteria). But what happened to those pitchers who had great stuff and a poor K/9? What about the flip side of that – the pitchers with poor stuff, but great strikeout results?


A quick refresher once again – command refers to the ability to “paint the black”. It is measured in called strikes above average – the upper third of the league was at 0.4 CSAA, median was -0.2, and lower third was -0.8 CSAA.

Great Stuff vs K9 results (command – CSAA)
Poor K/9 OK K/9 Great K/9
Poor Stuff 0.39 0.17 0.62
OK Stuff -0.27 0.18 -0.24
Great Stuff -0.81 -0.12 -0.73
SOURCE: Baseball Prospectus
minimum 30 innings pitched in 2017, total 451 pitchers
 So, the guys who had great Stuff, but produced poor strikeout results had the worst command of this group, generating -0.81 called strikes above average on the outside of the zone. Those who had poor stuff, but a great K/9 – unsurprisingly, they had the best command, getting on average 0.62 called strikes above average on the black.
What is a bit surprising is, those who had great stuff and great K/9 also had fewer called strikes above average – but there appears to be a reason for this.


Control is defined as the percentage of the time a pitcher throws a pitch inside the strike zone. Doesn’t matter where – just as long as it’s a strike.

Great Stuff vs K9 results (control)
Poor K/9 OK K/9 Great K/9
Poor Stuff 45.64% 45.80% 44.03%
OK Stuff 46.23% 45.18% 45.95%
Great Stuff 46.66% 46.52% 46.72%
SOURCE: Baseball Prospectus
minimum 30 innings pitched in 2017, total 451 pitchers

Those with the best Stuff and the best control had the best strike out rates. Essentially these pitchers are saying – enjoy your shortened period of synaptic connections, good luck making contact.  Those with poor stuff and a great K/9 kept their pitchers out of the middle of the zone. That sounds like a great way to survive.

Case Studies

So, what went wrong for guys with great stuff?

Reynaldo Lopez has great stuff – his fastball velocity is above league average (94.63 mph), and his pitches separate well in velocity (17.5%). However, his separation between pitches is right around league average – 12.9″ (compared to 13″). Looking at his command, he’s averaging 4 less called strikes compared to league average. Well, there’s one strikeout right there…  He also keeps the ball in the zone close to 50% of the time, compared to the league average of 45.9″. Yeah, elite velocity is hard to hit – but when that pitch stays in the zone a lot, doesn’t paint the black, and the stuff arsenal doesnt’ separate a lot – you won’t miss a lot of bats.

Jesse Hahn is a bit more of the same – elite stuff, but a very low K9. His fastball is just above league average (93.7 mph), and his distance separation is elite – 23″ (compared to 13″). However, the change in velocity is only 10%, and he gets 2 less called strikes than average. Pair that up with the ball being in the zone an above average amount of time (50%), and there’s a recipe for bats to get in the way of the catcher’s glove.

This story gets repeated for Matt Boyd, Lucas Giolito, and Jeff Hoffman – young pitchers with great stuff, but results in the strikeout department that are to be desired. The ball gets left in the zone, doesn’t nibble the corners, and above average velocity can often be offset by small separation between pitches.

Daniel Mengden is really an interesting case study in this exercise – his command is pretty much in line with league average – just slightly below, with 0.7 less called strikes compared to average. He’s got an average fastball, but great separation for both velocity and distance. Are the signs there for Eno Sarris’ adopted son to finally break out in 2018?

Michael Fulmer has elite fastball velocity – 95.8 mph – but pairs that with only 8% change in speeds, and 11″ of separation between his arsenal. He gets nearly 2 less called strikes than average, and keeps the ball in the zone for 48.5% of his pitches – great fastballs, no matter how great they are, tend to get hit when they stay in the zone that frequently. Fulmer’s path to elite status may be gated by adding one more pitch – something that breaks away from his fastball, and creates more space for swinging strikes.

Keep Stuff in mind for your keepers – it may represent a skill set that requires a slight tweak, and rewards may follow.

We hoped you liked reading When Good Stuff Goes Bad by Mike Sonne!

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Ergonomist (CCPE) and Injury Prevention researcher. I like science and baseball - the order depends on the day. Twitter: @DrMikeSonne

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