I'm guessing you never played contact sports 
I played both forms of football, and I have to say, what people call "soccer" is far more tiring, and does take more energy/athleticism.
What people don't realize is that if anything, american football is more of a strategy game between the coaches with athletes as game pieces.
And no, I didn't play kicker, played D-Tackle in high school (tied for most sacks in division), also was goalie for 3 years until injury.