How many games a week does he bowl???
The thumbhole may not be horribly tight - the span may be stretched, or the pitches a little "different" than the build of his hand might indicate - causing friction and callous buildup.
You bowl 10 a week - he probably bowls 150.
If Pete and I have anything in common, that "tight" fit helps control loft and release timing. If you get out of the ball too soon, it can really mess up your day.

I believe that many of the pros like a tight thumb (and sharper holes) than amateurs to keep them from grabbing the ball.

From Ron's tips:

The first step in learning this release is at the very beginning, with your grip on the ball. To have a good, clean, consistent release, it’s imperative that you don’t squeeze the ball in your stance. The holes in the ball are called “gripping holes” and that is the worst thing we could have ever called them. You need to hold the ball like you are holding a baby bird or an egg in your hand. If your ball fits properly you should not have to squeeze the ball anywhere in the swing or during the release. If the ball wants to slide off of your thumb, unless you squeeze it, then add tape or Ron C’s Magic Carpet to the hole to snug it up.  If your thumb wants to slide out no matter how tight you make your thumb, then have your pro shop check your pitches. You may have too much reverse pitch or some other improper fit. Remember, if you squeeze the ball, you have to subconsciously tell yourself to let go. There is no way you are going to be able to do that the same every time. The more pressure on you to make a good shot the more likely you are going to hang on to the ball too long.


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Ron Clifton's Bowling Tip Archive