I'm sorry; butterflies isn’t a very good lift for football. I would have to say squat, all core exercises, bench and exercises that build fast twitch muscle fibers (speed squat, speed bench, band squat, band bench, chain squat, chain bench, etc.). I agree with whoever said that you can't mimic football in the weight room, so what do you do? You get as fast and as strong as you can doing your major lifts (bench, squat, deadlift, etc.). Just my 2 cents.