Complex sentence: Saito was marked as a top prospect by NPB scouts from his days at South Kyoto High School; he, current Hiroshima Carp pitcher Masayuki Hasegawa and Saitama Seibu Lions pitcher Tomoki Hoshino were dubbed the "Big Three" of their particular age group.
Split into simpler sentences: Saito was marked as a top prospect by NPB scouts from his days at South Kyoto High School. He along with the current Hiroshima Carp pitcher Masayuki Hasegawa and Saitama Seibu Lions pitcher Tomoki Hoshino were dubbed the "Big Three" of their particular age group.