The knuckleball is one of baseball's most mysterious pitches because its moves unpredictably on its way to the batter.
It's very difficult to master, but when thrown properly, it's difficult to hit as well. The pitch is thrown like a fastball, but because of the way its held and released, the ball has almost no spin.
Dave Clark is the author of "The Knucklebook: Everything You Need to Know About Baseball's Strangest Pitch." For research, he interviewed a number of successful knuckleball pitchers including fomer major league all-star Charlie Hough. Hough told him that the best knuckleball is one that barely rotates between the pitching mound and home plate.
"What he discovered through experimentation" says Clark "is that if the ball rotates ever so slightly, between a half and a quarter of a turn or so, and straight forward, that seems to be giving the best movement and action that he (Hough) finds."
The irregular movement of the pitch is caused by the changing aerodynamics of the ball as it moves through the air. That's because the stitches on a baseball create more drag than the leather.
A normal pitch, like a fastball or a curveball, spins rapidly as it leaves the pitcher's hand and the textural differences on the surface of the ball are evened out. But as a knuckleball slowly rotates, it presents a new pattern of stitches and leather to the air it is moving through and those shifting aerodynamics cause the ball to change direction.
The knuckleball got its name because the first pitchers to throw it, a hundred years ago, actually placed their knuckles on the ball as they released it. Modern knuckleballers, like R.A. Dickey of the Twins, use a different grip.
"And the way that I hold it," says Dickey "I just kind of grip it with my fingernails on my pointer finger and my middle finger and I dig my fingernails in right behind the horseshoe of the baseball and let it go from there."
After ten years of limited success as a conventional pitcher, Dickey switched to the knuckleball three years ago. He believes the Metrodome is an excellent place to throw it.
"I pitched there last year with the Mariners" Dickey explains, "and I found that that constant climate where you have a little bit of humidity in the Dome and a little bit of air conditioner in your face proves to be a real nice kind of controlled atmosphere to throw it in. Whereas if you're on the coasts somewhere and you get wind gusts up to 30 miles an hour, it could be a little more difficult sometimes."
There's other evidence that the Metrodome is conducive to knuckleballing.
Tim Wakefield of the Boston Red Sox has been the best knuckleballer in baseball for years. His record in domed stadiums is substantially better than it is in open-air facilities. "Knucklebook" author Dave Clark says a dome helps a knuckleballer keep his pitches in the strike zone.
"What you've got is something very unique indoors" says Clark. "You've got consistent air flow. It's exactly the same all the time and cutting out one variable in what you're trying to do out there on the mound is certainly going to be a big help."
Over baseball's long history there have only been a few successful knuckleball pitchers at the major league level. That's because it's so difficult to master and control, but also because most pitching coaches and managers don't understand how the pitch works. Dickey says that forces a knuckleball pitcher to be self-reliant.
"A lot of times you kind of feel like the kicker for an NFL team," says Dickey, "where they put you on the back field and have you join the rest of the team when it's time to do your thing. Because it's such a unique pitch and such a small fraternity, you almost feel a little bit like you're alone."
But Dickey says his teammates and Twins fans will be very welcoming as long as his knuckleballs are getting hitters out and helping the team win.