One of the most important things to remember when you are describing something or someone is that you must SHOW and not TELL about them. If you are going to say that Michael Jordan was a good leader, then you need to come up with evidence that proves that. If you are going to say that Brett Farve is the best quarterback ever, then you need to show what he has accomplished that other quarterback's haven't.
A literal description of activity can be as poetic as metaphor and symbolism. If you were to detail the entire process of muscle and bone that goes into a Football Kickoff... well, it could be dry and boring, or you could really get into the sinew and membranes and make it something amazing to read. I can see it now:
Electrical signals speed down the nervous system; outside the body, no time at all has passed, his foot frozen in midair. The contracting muscle senses the changing attitude, halts its motion, and even in real-time, for just a moment, the man stands still. Then the muscle extends, pushing against the hip and knee as the foot fires out, impact, and now the signals change again, and again, a thousand times each second....
Anyway, that's where I'd go, but I tend to the literal. The issue would be keeping it interesting instead of dry.
Metaphors are always a creative tool to use when describing a person/place or thing. By using a metaphor, you are detailing your understanding of the literary device and supporting your ability to compare two things which would not typically be compared.
As for athletes in particular, it is usually their personality and their team affiliation that attracts me more than their accomplishments on the field. I am a big fan of Tim Tebow--not because of his religious views, but because I am a University of Florida grad; because of his larger-than-life persona; and because of the exemplary manner in which he managed to conduct himself during is four years in Gainesville. The fact that he continues to prove his detractors wrong with his great work ethic in the pros makes me admire him even more.
I guess I admire all athletes, because I know the dedication required to be a good athlete. As a subset, I admire student athletes, because as a teacher I know what they have to do in school and I can't imagine how they can apply themselves so well both at school and in the sport.
You can focus on one particular achievement and describe that in detail. This can be used as a mode of synechdoche where your example serves to describe the larger qualities of the person you are focusing on.
For example, you could write about how writing Moby Dick put all of Melville's interests and talents on display while also showing his personal challenges as a professional writer and as a story-teller.
Or you could write about Kobe Bryant's first NBA Finals MVP award and how that particular achievement exemplifies his character and his story in the NBA.
Going off of something that Post #4 says, I think that the best way to do this would be to discuss what your own life would be like if it were not for this person. She talks about how the world as a whole would be different, but I think that this is a more personal issue. I think that you should relate it to yourself and try to talk about how your own life would be poorer were it not for this person you admire.
Post #3 has some great suggestions. Your question is so broad, there's a multitude of possibilities.
You could present descriptions of scenarios - specific incidents in which your athlete/hero was involved, explaining what happened, what the person did - and follow the descriptions with the reasons why you respect the person for taking those actions.
You could predict how the world might be different if your person had not lived or had not done whatever it is that you admire. How would our world be different if Benjamin Franklin had not used a kite and a key to explain electricity?
There is no proper way to do this. So, creativity is the way. In view of this let me list a few ideas.
First, you might want to compare your favorite athlete or person to another great historical figure. For example, Plutarch the great ancient biographer did this to great effect. So, if you like someone like president Obama, you might want to compare him to Martin Luther King Jr. or Abraham Lincoln. Comparisons can be extremely powerful and creative.
Second, you might want to pick one aspect of the person you are writing about and expand it and look at it from various perspectives. This can be fruitful as well, especially if this something is not well known at all.
Third, you might want to be more creative a write a poem or song that describes your favorite person. By doing this, you can introduce myths and other creative forms.