Complex sentence: Violinists and violists may develop calluses on one side of the chin due to pressure exerted by the chin-rest of the instrument when playing, before this callus develops, players may experience neck pain and blistering of the chin.
Split into simpler sentences: Violinists and violists may develop calluses on one side of the chin due to pressure exerted by the chin-rest of the instrument when playing. Before this callus develops, players may experience neck pain and blistering of the chin.