Bowling/inside the ball
What do they mean by holdin g the ball inside
Delivering a ball, especially when looking to get it to hook, necessitates rotation. Getting the ball to hook more requires a hand position that finishes to the side of the ball. More rotation is achieved when the hand position creates more spin. So starting inside of the ball allows for more rotation.
Let me try to explain where your hand can be when rolling a ball. If you hold a ball with the crease of the elbow facing forward, your palm facing forward, the ball would roll out of the hand, from that position, with minimal axis rotation, often described as "up the back" of the ball. Hand action, or moving the ball with hand/wrist as you deliver a shot, ideally achieves a position where the hand is to the (out)side of the ball (palm turned inward toward your ball side leg, up to 90 degrees). Going from the palm forward to palm turned 45 degrees, is a typical finish position for many, many bowlers. To strengthen the finish and roll of the ball, starting the "hand action" from a stronger position, the stronger position is more inside the ball.
To achieve that position, as you swing the ball back, various parts of your body can get the ball turned where the hand is more palm/thumb rotated to the right (for a right hander). In some players the shoulders open, elbow is slightly cocked, arm/elbow rotates open (to the right), pinky side of the hand is rotated up and outward slightly, the back of the hand is exposed to the leg. When swinging the ball, getting the ball into this position, allows the bowler to create more torque. So, getting to the "inside of the ball" as it swings back allows for more torque, stronger rotation, often a higher rev rate and more hook. I hope this helps.
Thanks for the question.