"Grad school" is what one does after one's initial university degree is earned, to go on for a masters or doctoral degree. As for the relative emphasis on athletics or community involvement, much depends on the school. Football is a huge preoccupation (not to mention big money earner) in some schools; other sports to lesser extent. At some schools, star athletes are often admitted and allowed to remain even when their academic performance is poor, just to help the team win. At any school, being good at a sport or even a musical instrument can help you gain admission, but usually it won't (at least it shouldn't) override poor academic performance. It then becomes more of a tie-breaker, or an argument to give you the benefit of the doubt if you are borderline otherwise. It might make a difference in your financial aid. (Remember how expensive college is for most Americans.)
Most schools - especially the better ones, like Ivy Leagues - also look for someone who is a well-rounded person and has dreams and motivation. It almost doesn't matter what you do: sports, music, scouts, debate, travel, art, started your own business, worked part time to support younger siblings, etc. As long as you did things outside of class, and made sustained commitments to something where you could better yourself and show accomplishment. They do also look for some investment in the community. Often these can go hand in hand, e.g. playing music at community events, mentoring younger kids in your sport or scout group, donating your business proceeds to a charity, etc.