'The Sing-Off' is back on NBC; an acapella singing competition. Home Free is the first country group on the show and they debuted with the longest running #1 song in history;  Florida Georgia Line's 'Cruise.'

'Cruise' wasn't the only country song on the show, The Princeton Footnotes, a group of guys, performed Taylor Swift's 'I Knew You Were Trouble.' Trouble is exactly what they got, being the first group sent home.

NEXT: Otto Tunes From Syracuse Cover 'Cups'

Syracuse A Cappella Group "Otto Tunes" Covers "Cups (When I'm Gone)"