Molina Barehand is named after one of the best defensive catchers of all time - Yadier Molina. He does this drill regularly and that where the drill comes from.
The purpose of the Molina Barehand is the train the catcher to catch the ball in the proper part of the hand. The ball should be caught between the thumb, forefinger, and middle finger because that equates to the proper place to catch a ball in the glove. If a catcher catches the ball with the palm of their hand 1) that hurts and 2) the ball is likely to pop out of the glove.
Additional benefits of this drill include building hand-eye coordination and training soft hands while receiving.
The catcher is in his/her primary stance and is holding a ball with his/her pinky & ring finger. You can see a close up of this in the picture below (Note: if a baseball is too large to hold comfortable in the catchers hand then use a bouncy ball, golf ball, or any small object that is able to occupy the pinky and ring finger and prevent the catcher from using them to catch the ball.)
The coach/drill partner is approximately 5-8 feet away.
The coach/drill partner tosses the ball nice and easy so the catcher has plenty of time to see where the ball is going and react accordingly. The standard version of this drill calls for soft, easy tosses so the catcher can focus 100% of catching the ball with their thumb under and a soft, quiet hand.
This drill should be practiced from both the primary and secondary stance.
To increase difficulty, the coach/drill partner can mix up locations throughout the strike zone. If the goal is to add velocity and challenge the catchers reaction time then it is recommended that tennis balls be used so the catcher doesn’t injure any fingers.