1) Certain slow pitch 2) Delivery 3) Fluttering baseball pitch 4) Fluttering pitch 5) Knuckler 6) Pitch 7) Slow pitch with a little spin 8) Unique slow pitch 9) Unpredictable pitch 10) Wavering pitch 1) Knuckler 
A knuckleball or knuckler is a baseball pitch thrown so as to minimize the spin of the ball in flight, causing an erratic, unpredictable motion. The lack of spin causes vortices over the stitched seams of the baseball during its trajectory, which in turn can cause the pitch to change direction—and even corkscrew—in mid-flight. This makes the p...
(from the article `baseball`) Relatively few pitchers use the knuckleball, which lacks axial rotation, making it subject to air currents. The ball is wobbly as it approaches the ...
[n] - a baseball pitch thrown with little speed or spin
A baseball pitch that is thrown to prevent rotation during flight. This causes the ball to break and move erratically.
A pitch thrown without spin, usually thrown with the knuckles, but even with the fingertips. It has a tendency to flutter and move abruptly and unsteadily on its way to the plate.
knuckler noun a baseball pitch thrown with little speed or spin