Complex sentence: After spending most of 1918 in the Navy due to World War I, he returned in 1919 only to develop arm trouble, finishing with a 3.83 ERA-the only time in his first nine seasons he posted a mark over 3.00.
Split into simpler sentences: After spending most of 1918 in the Navy due to World War I, he returned in 1919 only to develop arm trouble. He finished the year with a 3.83 ERA-the only time in his first nine seasons he posted a mark over 3.00.