The USDDN Steering Committee Executive Board has issued the following clarification on field dimensions.
Rule states the following
The competition field shall be a rectangular shape with a width of 40 yards and a minimum length of 70 total yards. A five (5) yard wide Challenge Zone has been created down the center of the field, extending from the 10 yard line to the 50 yard line.
To Clarify - While the Recommend Field Size is 40 x 70 yds, the Field of Play is actually 30 yds x 60 yds, as shown in the image below. The Recommended Field Size allows for a 5 yd clearing on all sides.
Super Pro Toss and Fetch field

TossFetch/Freestyle Recommended

We recognize that it is not always possible to locate a field that meets the recommendations. Therefore, the Minimum Field Size is 40 x 60, with a 30 x 50 Field of Play. This Minimum Field Size allows for a 5 yd clear zone on all sides as shown below
.Super Pro Toss and Fetch Minimum field requirements

Toss Fetch/Freestlye Minimum field requirements

