If you are given the responsibility to line a field, here are a couple of suggestions. To get a square pitch, first lay out one end line for the width of the field using string and a couple of stakes. Measure out 30 feet from the corner along the width. Measure 40 feet from the same corner along the length using your best guess for a 90 degree angle. Last, measure a 50 foot diagonal line to complete the triangle. Adjust the angle of the 40 foot line to match it up with the diagonal. See the diagram below:

You now have a square angle. From here you can lay out the rest of the perimeter. To draw the center circle place a stake at the center of the midline with string tied to it. Tie the spray can to the other end of the string with the proper radius and draw the circle.