In the media they portray sport personalities such as footballers as a negative way and only showing this way, this can influence people who are fans of the players or the team and follow them in their foot steps which can lead to others acting to other people in this, negative way.
Because all though he knows his sister is dead, he can still hear knocking and scratching sounds coming from her coffin. She's dead, but comes back to life to haunt him causing his madness to grow stronger.
