Very easy boss to defeat.
But also before you start shooting the boss you can shoot down the blimp above the stadium to get the 'sunday, black sunday' achievment as it is missable, but can come back to it later though.
You need to aim for the boss eye and his back, his eye and part of his back will be red and those are the areas you need to aim for.
Just keep shooting the rockets at these parts and avoid his blue lightning ball attack and when he jet packs across the football field at you.
When you run out of ammo some more will be dropped around the field so just look for the red flares which are where the ammos been dropped.
Once you've taken the bosses energy all the wall down his energy bar will start flashing and the boss will be lying on the floor, you need need to run over to the boss and press X which will make Duke jump on the boss where it will ask you to repeataly press A button to pull something off the bosses back.
Once thats done the boss will drop back down to the floor but dead this time and his eye will pop onto the floor.
You then just press X next to the eye and he will kick it for a field goal.
The achievement will then pop.