Group polarization refers to a certain tendency among group members, which strengthens the results and tends to extremes through the mutual influence of the group, thereby deviating from a certain rationality phenomenon. There are usually two cases of group polarization. One is to make the result more adventurous or even radical, called risk migration; the other is to make the result more conservative, called cautious offset. According to the above definition, which of the following phenomena does not involve group polarization? ['A slightly flawed movie was rejected as useless in a web forum.', "After a vote, the defense committee unanimously rejected a student's doctoral dissertation defense.", "Everyone keeps silent about someone's bad behavior, which makes him even more arrogant.", 'Team A was penalized for a foul during a football game. Team A fans expressed great dissatisfaction and threw debris into the field.']