Greatest

From Ultipedia

A greatest is a play that involves jumping from within the field of play to beyond the sidelines in order to catch the disc and then releasing a throw before landing (or touching anything out of bounds).

It is typically an unplanned desperate move, but when successful it can be spectacular.

[edit] Explanation

As a player is considered 'in bounds' until touching something that is 'out of bounds' a player still in the air, but outside the field of play is still considered 'in bounds' if they jumped from within the confines of the field of play.

[edit] The name

This move is called the Greatest, because if you can do it, you are "The Greatest."