Small triangular formation of lights performs flight display then vanishes over playing field.A small (8 feet) equilateral triangular formation of faint green lights flew past me from north to east at about 30 feet in the air. As it went past me into the field to my left it performed a loop the loop type maneuver then continued into the filed for 60 feet or so and then vanished. There was no discernable craft, just the lights, although they appeared somehow to be joined together. At first I thought it was birds but that was soon proven to be unlikely because of the way it flew. The whole thing lasted about 9 or 10 seconds and had a very unearthly feel to it, perhaps because of the silence and ethereal appearance of the lights. I had the feeling it was somehow displaying, like it wanted me to see it.