Complex sentence: In 1975, he missed most of the year with an inner ear infection, which effectively ended his days as an every day player until mid 1977 through the end of 1980, when he was the Yankees' regular outfielder/DH.
Split into simpler sentences: In 1975, he missed most of the year with an inner ear infection. From mid 1977 through the end of 1980, he was the Yankees' regular outfielder/DH.