Complex sentence: On the 1974-75 NBC series Lucas Tanner, Hartman played a retired baseball player turned unconventional high school teacher; the series'cancellation marked the end of Hartman's acting career.
Split into simpler sentences: On the 1974-75 NBC series Lucas Tanner, Hartman played a retired baseball player turned unconventional high school teacher. The cancellation of his series marked the end of Hartman's acting career.