Simplify the following text for a Grade 13 native English-speaking person.
Original: Led by a charismatic Friends of SNCC student activist named Mario Savio , upwards of three thousand students surrounded a police car in which a student , arrested for setting up a card table in defiance of a ban by the University , was being taken away .
Simplified: Led by a Friends of SNCC student activist named Mario Savio , more than three thousand students surrounded a police car where a student , arrested for setting up a card table against a ban by the University , was being taken away .