Complex sentence: The song made its debut on the 2014 Billboard Music Awards on May 18,2014 with a performance by Lambert and Underwood; they performed the song again at the CMT Music Awards on June 4,2014.
Split into simpler sentences: The song made its debut on the 2014 Billboard Music Awards on May 18,2014 with a performance by Lambert and Underwood. They performed the song again at the CMT Music Awards on June 4,2014.