Complex sentence: Their arch rivals are their neighbors to the east, Billerica, whom they play every year in football on Thanksgiving Day, other rivals include Lowell, Dracut, Andover, and Tewksbury.CHS does have one out of conference rival, which are the Acton-Boxboro Colonials.
Split into simpler sentences: Their arch rivals are their neighbors to the east, Billerica, whom they play every year in football on Thanksgiving Day. Other rivals include Lowell, Dracut, Andover, Tewksbury and an out of conference rival, the Acton-Boxboro Colonials.