Complex sentence: An unnamed Potential Slayer girl is "activated" during the events of "Chosen", violently thrown on her back by the calling before saving the lives of her schoolmates from a runaway truck with her newfound Slayer powers.
Split into simpler sentences: An unnamed Potential Slayer is activated during the events of "Chosen". She is violently thrown on her back by the calling but then saves the lives of her schoolmates with her newfound Slayer powers.