There is racism and there is political correctness. This falls under the extreme category of political correctess, where you apparently can't use physical characteristics to identify someone. What if she had red hair and the announcer said; "Clement - the woman with the red hair - has superior footspeed and should strike hard in the last 200m"? That wouldn't be offensive at all, and neither should identifying her as an African-American.
As for the "Why can't she just be called an American? Why Make her only half an american?" argument, thats stupid. Many people are called Irish-American, Italian-American etc. Because the U.S.A. is a country of immigrants, hyphenations are often used to distinguish race. The descendants of slaves have cleary changed from their ancestors to become a different "race", and thus are designated so.
Finally, for the argument saying "Blacks are better at sports" is just as racist as saying "Blacks are dumb" is equally or moreso retarded as the rest of filth spewing from politically-correct whackjobs mouths. Something is only racist when it denotes hatred towards a certain group. Complementing West-Africans, and thus African-Americans on their superior genetics is not an act of hatred. Saying blacks are uneducated, something that brings back racial predjudices and human rights violations from American history, has a little bit more hatred behind it.
Its the same reason why the word "N*****" denotes hatred and is unnacceptable, whereas the word "Cracker" does not stem from any time where whites were horribly mistreated and the word itself was not used to demean human life.
Except maybe on the basketball court.