Complex sentence: Probyn was fairly slight for a modern international prop, and a good part of his effectiveness can be explained by his unusual physique: his bony shoulders sloped at a sharp angle, and his hips were widely set.
Split into simpler sentences: Probyn was fairly slight for a modern international prop and a good part of his effectiveness can be explained by his unusual physique. His boney shoulders sloped at a sharp angle and his hips were widely set.