gyroball
A forkball typically drops and wobbles in the direction of the throwing hand, but by adding gyro rotation, the gyro fork can be made to drop straight down.
The advantage of dropping straight down is that it becomes harder to distinguish it from a four-seam fastball, and it is less affected by the batter's handedness (right-handed or left-handed).
Gyro rotation is a type of spin that is less affected by air resistance, which might seem incompatible with the forkball, but because the rotation speed is relatively low, it doesn't have much impact.
Grip and Release
For the gyro fork, the gyro spin is applied with the index finger, so the index finger is placed on the seams of the ball.
While the ball is gripped between the index and middle fingers, similar to a normal forkball, the key difference is that during release, you want only the index finger to catch the seams, so the middle finger should not be placed on the seams.
The arm motion and wrist usage are the same as with a forkball.
The arm swing should be similar to a fastball, avoiding the use of the wrist.
During release, the ball should slide off the middle finger side, while the index finger side, where it is placed on the seams, catches the ball.
It is difficult to achieve a perfect gyro spin, but the closer you get to the desired gyro spin, the more effective it will be, so practice is key.