Complex sentence: City leaders adopted the moniker "The City of Champions" after the Alabama Crimson Tide football team won the BCS National Championship in their 2009,2011, and again in their 2012 seasons, before going on to win the College Football Playoff in the 2015 season.
Split into simpler sentences: City leaders adopted the moniker "The City of Champions" after the Alabama Crimson Tide football team won the BCS National Championship in their 2009,2011, and again in their 2012 seasons. The Tide then went on to win the College Football Playoff in the 2015 season.