Matt Waldman's RSP NFL Scouting Glossary defines Clapping/Gator Catching, a sub-optimal technique with hand positioning for wide receivers. 

Why Is Hand Positioning Vital for Receiver Play?

The shape, spin, trajectory, and velocity of a thrown football require a pass catcher to attack the target with methods that allow the receiver an opportunity to achieve several objectives.

Meet the ball at the earliest point of arrival.

Slow the spin of the ball in a controlled manner that reduces the potential for a violent recoil.

Make the catch with the first attempt to maximize efficiency.

Optimal hand positioning creates easier second-chance attempts to win the ball.

Secure the target quickly enough to reposition the ball away from tight coverage.

Secure the target quickly enough to maintain the path of the route and maximize yardage after the catch.

A football travels at a high speed and the spin isn't always tight. Combined with the oblong shape and texture, there are several challenges for a player that don't include the position of the defender and/or the intensity of contact that the defender will deliver as the receiver attempts the catch.

What Is Optimal Hand Positioning to Catch a Football?

The optimal receiving techniques begin with the fingertips. Because of the ball's spin and shape as well as the speed a quarterback can deliver it, the ball is prone to a violent recoil with it strikes a singular, flat surface. Throw a football against a wall and watch how violently and unpredictably it rebounds from the surface.

The same thing happens when the ball strikes the palm of your hand — a singular, flat surface. The fingertips are marvels of human engineering because when 6-8 of them meet an oblong object that's arriving with great velocity and high RPMs, they have the precision to apply subtle pressure that stops the spin.

If the precision of the fingertips working in tandem isn't perfect, it will still reduce the spin to a manageable movement — a soft and slower recoil that's easier to track for a second attempt at the ball compared to the ball recoiling violently off the palms, chest or helmet.

The best way to position the hands so the fingertips can stop the spin and control the ball depends on the trajectory of the target. If it's a target above the waistline, the hands should be extended outward with the thumbs and index fingers forming a triangle.

This isn't a perfect representation because the hands should be cupped a little more so the rest of the fingertips are in a position to grip the target, but you get the basic idea.

 

If the ball arrives below the waistline, the hands should be extended outward with the pinkies together as if you're holding them together to cup food.

Gator-Catching/Clapping: A Common Technique Error

Watch a young child learning how to catch a ball it's common to see them attempt to clap their hands onto each side of the ball. It's a logical idea but an inefficient one because it requires a lot more timing and coordination to meet a moving object with both hands traveling from opposite directions than it does to have your hands in a fixed position as the ball arrives.

It also encourages initial contact of the ball with the palms rather than the fingertips and this leads to a violent and unpredictable recoil. If the hands miss completely, the ball has a violent recoil off the surface of the receiver's facemask or chest.

Although college and NFL receivers have spent hundreds if not thousands of hours catching the football, there are scenarios that influence a receiver's lapses with catch technique:

Mistracking the trajectory of the football and forced to re-adjust at the last moment.

The receiver is focused on a different task that disrupts their timing and flow.

The target is arriving at a spot where either hand position is viable and leads to indecision.

The receiver has to make an athletic adjustment over or around a d...