Complex sentence: Attendance of 14,975 and 15,240 at two heated contests against their then arch rival, the Seattle Thunderbirds, assisted the Rockets in chalking up the highest per game average for a first year expansion team under the Canadian Hockey League umbrella.
Split into simpler sentences: Attendance of 14,975 and 15,240 at two heated contests against their then arch rival, the Seattle Thunderbirds. This assisted the Rockets in chalking up the highest per game average for a first year expansion team under the Canadian Hockey League umbrella.