An invertible mound assembly for a game field, to convert the game field between activities such as baseball that require a raised mound and other activities such as soccer or football that require a continuous flat field surface. An invertible mound body having a raised surface on one side and a flat surface on the other is supported on a base structure in a recess in the game field. When disposed downwardly the raised surface is received in the recess while the base structure supports the flat surface of the mound body level and flush with the surface of the game field. When inverted and placed back on the base structure, the flat surface of the mound body is disposed downwardly and the raised surface of the mound body is disposed upwardly to form a mound that projects above the level of the game field.