With respect to hiding the ball, it's common practice to hide the ball while IN your glove.
Using the glove to SHADOW the ball in your hand.. up to the high "prop" position .. has always been a refinement that hasn't met with any degree of effectiveness due to the poor to very poor conditions of the pitching mounds found on most - if not all, play grounds, high school ball fields, and public parks. However, that's not discounting those players that can. Some pitches are very effective with using their glove, body and so forth, regardless of the poor surface conditions that they're working off of.
Your glove, its fit and comfort, playability, its balance contribution to your particular style of pitching is a refinement that a lot of players take for granted. Below is a suggestion for you with respect to your hand's posture and the glove's fit.
Gloves and Glove Hand
If you’re serious about baseball, you must consider your choice of a glove(s) as an important part of your presence. However, for most amateur players, any glove will do – and that’s ok. If that’s the case, have a great time, enjoy the game and skip this part.
For the serious competitor – read on. Your baseball glove provides you with two things. First, it’s your playmaker that will catch and trap baseballs. Second, it supports your balance and stability while going through your delivery motion.
For play making, most pitchers prefer a twelve inch (12) glove, as oppose to a larger glove – like an outfielder’s glove. The twelve inches are measured from the base of glove to the tip of the longest finger on the glove. The pocket of the glove should be deep enough to hold the ball – but not trap it so it can’t be removed quickly. The stretch of leather that’s sewn between the first finger and the thumb is called the web section. This web can be either a closed weave or an open weave back. Many pitchers prefer a closed weave back.
With respect to your overall balance and stability, the glove contributes more than you think. To begin with, your glove acts like a counter weight – initially - on a part of your body that’s shifting its momentum forward. Then, as you complete your delivery, your glove assists with your follow through motion. In addition, certain mound conditions may dictate different gloves of style and weight – a refinement most amateurs overlook.
All pitchers must choose a glove that conforms to the hand with a smooth form, as appose to a claw form found with gloves worn by infielders. In other words, the glove’s pocket and finger section should be somewhat open, not scooped. The main reason being is that the glove hand must be relaxed enough so the tendons and muscles in the wrist and arm can accept the rotating motion of the shoulders, thus pulling back and completing the proper follow though during a pitch. If the glove forces the hand to assume a claw posture, this puts stress on the tendons and muscles of the glove arm. A closed and straight-fingered hand relaxes the tendons and muscles of the glove arm. Try both hand postures yourself and you’ll see exactly what I mean. First try the claw posture and see if your glove arm tucks in comfortably while you rotate your shoulders and finish your delivery motion. Then try the other posture.
Courtesy of “Pitcher’s Notebook for Amateur Play – Rookie Edition” 2007