For this you need the formula for a circle:
A=πr2 (pi r squared)
You know the diameter is 50 yards, so the radius will be half of the diameter.
A=π(25) squaredA=(3.14159)(25) squared (remember to square before you multiply - order of operations)A=(3.14159)(25*25)
A=(3.14159)(625)A=1963 yards
Hope this helps! :)