Harper led off the fourth inning with a slow roller that second baseman Mark Ellis barehanded and flipped to first. The throw appeared to beat Harper, and umpire Jeff Gosney called him out.
The 21-year-old Harper kept his head down, screaming his displeasure as he passed Gosney on his way to the third-base dugout. Gosney threw out Harper, who didn't seem to initially realize he'd been ejected.
Harper turned in apparent disbelief to argue with Gosney, and Nationals manager Matt Williams joined in.
The game was delayed a few moments while Harper gathered his belongings and walked to the visiting clubhouse beyond the left-field wall.