On the 27th minute of the UEFA Champions League tie between Manchester United and Chelsea, it appeared to be game, set, and match. John O'Shea swung a great ball from the left flank to the edge of the six yard box, and it appeared the Chicharito had timed his run perfectly to stay onside as he ran onto the ball and headed it into the back of the net. However, the linesman flagged for offside, and Chelsea are still very much alive.
Upon looking at the slow-motion reply, it appears that the referee got his decision absolutely correct. Chicharito, though just by the narrowest of margins, was indeed offsides. Had he been six inches farther away from goal, he likely would have still met the ball in time, scored, and given United an insurmountable lead. Instead, it's still 0-0, and Chelsea are still just one goal away from forcing extra time.