I was at nationals park and during the national anthem, a bright green light went across the sky and was gone really quickly. i thought it was a plane at first, but planes move too slowly. the light was just above the scoreboard as i watched the national anthem be played and this cought my attention and darted across the sky. the light disappeared within 2 seconds or so. the only other thing that it could be would be a laser pointer, but a laser pointer of that high power would not be allowed in the park. so the only thing left would be a ufo.