Complex sentence: Later their makeout session is interrupted by Leo Balmudo, the leader of the Scorpions, a rival greaser gang of the T-Birds, who rear-ends Kenickie's car, insults them, and drives away.
Split into simpler sentences: Later their makeout session is interrupted by Leo, the leader of the Scorpions, a rival greaser gang of the T-Birds. Leo rear-ends Kenickie's car, insults them, and drives away.