Complex sentence: Kelly reported that the altercation with Lien was not the only problem involving the group on September 29, as over 200 other people had complained to the police about the reckless driving of the bikers on Manhattan's streets that day.
Split into simpler sentences: Kelly reported that the altercation with Lien was not the only problem involving the group on September 29. Over 200 other people had complained to the police about the reckless driving of the bikers on Manhattan's streets that day.