Complex sentence: The Boat Race is a side-by-side rowing competition between the University of Oxford (sometimes referred to as the "Dark Blues") and the University of Cambridge (sometimes referred to as the "Light Blues").
Split into simpler sentences: The Boat Race is an side-by-side rowing competition between the University of Oxford and the University of Cambridge. It is a side-by-side rowing competition between the University of Oxford (sometimes referred to as the "Dark Blues") and the University of Cambridge (sometimes referred to as the "Light Blues").