http://sports.espn.go.com/nfl/news/story?id=1632537
Rule 12, Section 3, Article 2 of the 2003 Official Playing Rules of the National Football League defines the unsportsmanlike conduct/leaping penalty as follows:
"Clearly running forward and leaping in an obvious attempt to block a field goal, or try-kick after touchdown and landing on players, unless the leaping player was originally lined up within one yard of the line of scrimmage when the ball was snapped."