Following the field line, there should be a line specifying the turf type and the distance to center field. Turf can be 1 (natural) or 2 (artificial), and the distance must be between 370 and 420 feet and divisible by 10. Field alterations cannot be made once games have begun. Example: FIELD 1 400 DONE would change the field to natural grass, with the fence 400 feet from home plate.