This article seems to be claiming that it's always a good idea to change speeds (so long as the batter isn't way off the previous one).

That seems quite counter-intuitive to me though: wouldn't pitchers have to mix over multiple pitch strategies in each situation, in order to keep the batter unsure of the coming pitch?

Perhaps the ideal mixed strategy would tend to change up the perceived speeds more often than not, but you've gotta mix in other pitches too, no?

Love the topic and always look forward to your articles, Eric. I used to pitch and find it interesting now to think about the science behind what I learned intuitively over the years.

On this topic specifically, I think this is exactly why hanging sliders are so dangerous. The sequence of low outside fastball-hanging slider would have similar perceived velocity, and of course movement on the hanging slider would be minimal. That puts the pitch squarely in the at risk category.

I think this also relates to the concept of "speeding up the bat" of a hitter, which you'll occasionally hear ex-player broadcasters refer to (I'm sure I've heard McCarver say this, which is telling given he was a catcher). That language never made sense to me, but the basic point was you don't really want to throw an offspeed pitch inside. I think this is the intuitive, player's way of describing what you're referencing in this article. "Speeding up the bat" doesn't literally mean anything, it just means the offspeed pitch loses a chunk of its perceived velocity differential when thrown inside, making it easier to hit.

I wonder if you have thoughts on something else that popped into my head a couple times as I was reading your previous articles. You discussed the effect of location on perceived velocity within the framework of the swing arc (i.e. you have more time to square up an outside pitch than an inside pitch). But I was wondering this, also. Does the location also make it more or less difficult to judge velocity and movement and react accordingly? I'm talking about perspective/angle on an object in motion. If it is coming directly at you it is much harder to judge its motion than if you have an angle on it. So an inside fastball is more difficult to judge, while an outside fastball is easier. Just to be completely clear, with the outside fastball you actually see it moving across your field of vision and getting larger within your field of vision. With a fastball straight between your eyes you can only determine velocity by judging the pace at which the ball is getting larger. The extra visual information on the outside fastball should make it easier to identify and hit. I don't think this add/subtracts perceived velocity, as you could misjudge the velocity in either direction, but it seems like it would disrupt timing in a disproportionate way, i.e. more for an inside pitch than an outside pitch.

Of course that is just fastballs where there is no/minimal break. With a breaking ball, it might be easier to judge the speed if it is thrown low and outside for the same reason as above, but the break may be more difficult to judge if thrown there because it would be occurring in the same plane as the hitter's eyes. This would give you the same poor read on the break as you have on the velocity of a fastball aimed right between your eyes. If the breaking ball is thrown inside, the velocity might be more difficult to judge, but you will have a better perspective on the break, so maybe net net it is easier to hit.

This all makes me think about why a good changeup is so effective. If you are a 2 pitch pitcher (fastball, breaking ball) and you throw a breaking ball away, the hitter can identify the speed, know it is a breaking ball, and decide when and where to swing (or not). If you also have a changeup, identifying the speed of an outside pitch no longer tells you everything you need to know about when and where to swing. You now have to read the break (or guess), which is difficult to do given your poor perspective on the break of a low outside pitch. An inside changeup would also be troublesome, but for a different reason. As mentioned above you have poor perspective on velocity on inside pitches, and while you have a good perspective on break, the break of a changeup looks similar to that of a fastball. So you really could have a difficult time identifying a good changeup no matter where it is located.

I'll stop rambling. Just curious whether you have any thoughts on this aspect of pitch location.