To throw a slurve, I took my 4-seam fastball grip, put my fingers together on the right seam on top of the ball. Then I moved my thumb up on the ball to the left, closer to my index finger. My ring and pinky were in usual position, on the side of the ball.
I threw the ball at full velocity, and snapped my wrist hard, like I throw my curve. The ball had a huge 3-8 movement. Almost completely horizontal, but it dropped a tiny bit. It must have moved around 12 inches to the left.
Another way to throw a slurve is to put your index and middle finger together, and place them on the top of the ball were the seams connect. Don't bend your thumb, the thumb should be on the bottom of the ball. Throw it like a slider.
You can also try to throw the ball with a curveball grip and throw it at a 45* angle. Or you can dothe football slider which is the same thing movement wise. If you throw one high, you'll get slammed.
Keep the ball below the waist at all times unless you're throwing it outside to a righty (for a right-handed person. Lefty, vice-versa). I've thrown it in a game a few times and it works decently if you can get it to work right.
Also the football slider is good for younger pitchers who haven't developed their arms. Cup the ball in your palm along the seams and throw it like a football.
Why You May Not Want To Throw A Slurve Ball?
The slurve isn't a particularly good pitch from a scout's perspective. It doesn't have the sharp bite of a good slider or the big break of a curve, making it really easy for batters with the opposite-handedness of the pitcher (not particularly eloquent, but you know what I mean) to hit hard.
Pro scouts will rate your breaking stuff higher if you throw a true curveball or a true slider, not a slurve. Just a word to the wise...
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