Complex sentence: In 2007, he finished the season with a 17--12 record but was left off the Red Sox roster for the World Series due to an injured shoulder that had been bothering him since late September.
Split into simpler sentences: In 2007, he finished the season with a 17--12 record. He was left off the Red Sox team roster for the 2007 World Series due to an injured shoulder that had been bothering him since late September.