Complex sentence: When Rose reached his senior year, he had used up his four years of sports eligibility, so in the spring of 1960, he joined the Class AA team sponsored by Frisch's Big Boy of Lebanon, Ohio in the Dayton Amateur League.
Split into simpler sentences: When Rose reached his senior year, he had used up his four years of sports eligibility. In the spring of 1960, he joined the Class AA team sponsored by Frisch's Big Boy of Lebanon, Ohio in the Dayton Amateur League.