this one took me ages to figure out cuz in the video he has his guitar dropped down a 1/2 step..
it goes
Trouble comes knocking I'll be ready alright
with my fists up ready to fight
But i ain't gotta put my fists up everytime
the Bm7 is hammered on from a barred 2nd fret..
the E is played open and the D is played barred...
just repeat that riff throughout..