Charlie Haeger is a practitioner of an increasingly-rare baseball art form. The 27-year-old right-hander is a knuckleball pitcher, meaning he lives and dies with the game’s most unpredictable — and often maddening — delivery. Few have mastered it, but when a knuckleball is thrown correctly and does its butterfly dance toward home plate, it is a thing of beauty. Haeger, who has made 34 big-league appearances, with four teams, was recently signed by the Red Sox and assigned to Double-A Portland.

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David Laurila: What is the key to throwing a knuckleball?

Charlie Haeger: First and foremost is being able to take the spin off the ball. Being able to throw a knuckleball isn’t something that a lot of people are able to do, just because you’re not familiar with it growing up. Basically, you have to make the ball rotate as little as possible.

Ideally, for me, would be half a turn, maybe three quarters of a rotation. With that, I can generate the best movement while still being able to command it. You can get away with ones that spin twice, but with anything over that you’re starting to mess with fire.

DL: How do you throw a baseball with little or no rotation?

CH: There is a particular way that I hold my hand, hold the baseball, and release it. But I don’t think there is one set-in-stone way that it has to be thrown. There is kind of a norm in the industry, although there obviously aren’t too many of us throwing one anymore.

What I try to do is keep my wrist as straight as I can when I let go of the baseball. I try to have my hand behind it, with my palm facing home plate.

My palm is [contacting] the ball, as well as two fingers — my index finger and middle finger. Technically, my nails are into the ball, not my knuckles. I kind of want the ball to pop out. That’s how you get it to leave your hand without spinning.

DL: How loosely, or firmly, are you gripping the baseball?

CH: It depends on the day. There are days where you want to hold it a little firmer, because it feels better to you, and there are days where you want to hold it a little looser. It’s such a feel pitch.

DL: Where are your fingers on the ball?

CH; If you look at a baseball, and where they write “Rawlings,” right underneath the horseshoe — both of my fingertips are pretty much right on the Rawlings. I try not to contact the seams. There are times where it feels better in a particular spot, but for the most part I don’t touch the seams. Any time your finger is touching a seam, you have a chance for the ball to be manipulated, just from catching a snag on a seam, or not letting go of the baseball in the correct way.

DL: Is there an ideal arm slot for a knuckleball?

CH: No, I think it all depends on who is throwing it. There are guys who throw it a little lower, and guys who throw it a little higher. I’ve moved my own arm slot, for feel, in the middle of a game, and even in the middle of an inning or in the middle of a hitter. I’ve played with it, just to see if one is moving better than the other. Normally, I’m pretty much over-the-top to three-quarters, a typical throw.

DL: How important are mechanics from the waist down?

CH: Just as important as they are for a regular pitcher. You’ve got to have your foot down on time. That’s a key for me. I have to have my left foot down on time to throw the baseball the right way consistently. Mechanics are a huge part of being a knuckleball pitcher.

DL: Does your thought process on the mound differ from that of conventional pitchers?

CH; My thought process is the same as any other pitcher. I’m trying to throw strikes and get guys out as quickly as I can. Baseball is hard enough, so I don’t want to make it any harder than it has to be. I think that a lot of guys overanalyze the game and over-think the game, and that’s where you can get into trouble. I try to throw strike one and get hitters out.

DL: Do you try to set hitters up?

CH: I don’t. Occasionally you get a chance to set somebody up with a fastball, or something along those lines. But for me, the beauty of it is that they know what’s coming. There’s no throwing a fastball up and in and then a slider down and away to set up another fastball in. It just doesn’t work that way with a knuckleball.

DL: What about changing speeds and moving the pitch in and out?

CH: I change speeds with it. The last game I was anywhere from 61 to 75, so I vary it. That’s something you have to be able to do to throw it well. You have to kind of use it like a regular pitcher uses his fastball and changeup. I don’t do anything with my grip, it’s just arm speed, and maybe my follow through is longer with the slow one.

[Moving the ball in and out] is something I try to do, but it’s a little harder to do that. Once it leaves your hand, you typically don’t have too much control over it. But there are days when I can make it go right and make it go left.

DL: To what extent can a knuckleball pitcher learn from another knuckleball pitcher?

CH: I think there are definitely keys and some mechanical issues that we go through. Our mechanics have to be pretty spot on to throw a consistent knuckleball. They have to be extremely repeatable. We have such a fine line. There is really no room for error for us. If you’re throwing a 68 mile-per-hour pitch up there and it’s not moving, you’re going to run into some trouble.

I’ve had a chance to work with Charlie Hough — I’ve listened to him a lot — so you can learn from them, but when it comes to the actual feel of letting go with the pitch, you’re completely on your own. Mechanically, there are definitely some things you can learn from other guys, but whatever you feel when you’re letting go of the ball… nobody else can tell you how to feel.

DL: What do you know about the knuckleball that you didn’t when you first started out?

CH: I understand it more. This my seventh or eighth year throwing one and I understand it now. I understand that some days are good with it and some days are bad. That just comes with experience. Early in my career I would get frustrated and would try to change something, and now I‘m more patient. I’m obviously always trying to improve, but I understand that I’m throwing a pitch that sometimes moves a lot, and other times doesn‘t move. I’m kind at the mercy of it.

Being a knuckleball pitcher is different from being a pitcher who throws a knuckleball. There are guys who throw one occasionally, or even half the time, but it’s hard to be a conventional pitcher with a knuckleball. You have to make a commitment to the pitch.