Fields are pre-built backgrounds for your plays and formations that give you a variety of field positions, player sizes, and field markings to choose from.
Like themes, fields are independent from the play/formation itself so you can change the field for your play at will. This makes it easy for pro subscribers to copy a play from the play library and modify it to match the other plays in their playbooks.
For example, as a high school basketball coach you might see a basketball play that you like but it’s diagramed over an NBA court. You can copy the play and change the court to High School, preserving the playart but moving the three-point line in to match high school court dimensions.