I have a 13 yr old son who has developed a bad habit of wrapping his swing behind his body the step before he releases the ball causing him to be very inaccurate and inconsistent. Any advice?

I'm going to take a wild guess and say he's trying to go coast to coast on the lane.

If you were to toss a Nerf football in the air with a tight spiral, you have to pivot your hand from left to right to achieve that. His back swing is similar at the release point in that his body is trying to pivot the hand under the ball to rotate it out. Not how you hook a ball properly, and quite a few people learn this way.

If you try to have him relearn how to stay behind the ball through the swing while maintaining a strong hand position up the back of it, that should go away naturally.

If he's not trying to swing the lanes, maybe he's trying to clear his trail leg by going around it, which is taking the ball behind his back, requiring it to figure-8 it's way through the swing.

Hard to tell without seeing him bowl though.
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There is nothing so easy to learn as experience and nothing so hard to apply.

Assuming he's right-handed, have him push the ball on his first step (or 2nd step if he's a 5 stepper) towards the 7 pin.  Everything else depends on not muscling the ball through the swing.  He should be doing just enough with his shoulder to keep the ball from falling wildly towards the floor.

Practice, practice, practice.
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Scolaí

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