Korea had a freekick in the first half that was weakly hit straight to the keeper. Sanchez caught the ball and then tossed it about 10 yards out in front of him as if preparing for a free kick or goalkick.
Problem was, there was no stoppage of play, and he just stood there and watched a Korean player grab the ball and put it in the goal.
The match ended 1-0 for Korea.
Sanchez supposedly heard a whistle and thought there was an offsides call, but if there was a whistle it must have been from the stands. It looked to me like maybe he just accidently tossed it a lot further out than he meant to, then tried to play it off when he saw that the Korean was going to take the ball.
Whatever the case, it was inexcusable, but as a US fan I had to laugh.