Complex sentence: The Clemson Tigers won the national championship, the second in school history, by defeating the Alabama Crimson Tide in the 2017 College Football Playoff National Championship, which was a rematch of the 2016 edition won by Alabama.
Split into simpler sentences: The Clemson Tigers won the national championship, their second in school history, by defeating the Alabama Crimson Tide in the 2017 College Football Playoff National Championship. The championship game was a rematch of the 2016 edition won by Alabama.