Haunted University

This is a story i read from somewhere but i forgot. This story is about a night class in University. I dunno which University because the writer didnt reveal the name of it. Here it goes, a guy and a group of his friends went for night class and headed to a room. On the way to the room, which is next to the field, they saw a ball, i think its a soccer ball in the field. They did not sense anything amiss and just went for the night class. When the professor was teaching, the ball suddenly rolled into the back of the class via back door. All the students were looking at the ball and some were in horror. Some might have already sense something was wrong with the ball. The professor was annoyed because his class was disturbed by a ball and furiously, he kicked it out of the room and the ball landed on the field again. Then, the lesson was on as usual. Not long after that, the same ball rolled into the class again via the back door. The students were in horror this time but the professor asked them to ignore the ball and concentrate on the on-going lesson. When the professor was teaching and he looked to the back of the class, he was paused and still. He was in horror too. He called the day off and straight went to his car and went back home. The students were confused and the ball was still there. They dare not to touch the ball and everyone went back to their hostel rooms. The following days, the professor was absent due to sick leave and it caused a stir in the U regarding what the professor saw that night. According to a source, that night, the professor was looking at the place where the ball was in the back of the room and saw a figure siting at the back of the room. The figure was actually the professor himself and the figure was smiling and grinning towards the professor. A doppelganger, i assume...!