Step 1: Grab the Close Seams
the seams that come close Together, face those towards you.
Step 2: The Grip
To grip this curveball, take your Regular Four seam grip, move your fingers together, And off to one side of the laces. Also put your thumb underneath your fingers.
Step 3: How to Get Spin
Next, to get spin take your grip in your hand and turn it so it looks like a backwards see. This is how you are going to get spin. when it is up high snap down with your grip to go from the first Picture to the second picture.
Step 4: Reasoning
The reason this doesn't hurt your arm, is because there is no twisting involved. it is all like a regular throw just snapping of the wrist, compared to the twist if a regular curve.