Watch carefully about 10 seconds into this video. You can see Melissa Tancredi of Canada step back and to the side with her left foot, tagging Carli Lloyd in the head. It definitely looks deliberate.
The play happened just as the second half was starting, while the ref's back was turned and Lloyd was already on the ground.
Before I hear another Canada team fan complain about bad ref calls, consider how the team would have done if this has been properly called. A red card would have taken this top player out for the game, leaving Canada playing a man down for nearly 40 minutes. http://www.nbcolympics.com/video/soccer/highlight-melissa-tancredi-stomps-carli-lloyds-face.html