The vast majority of African Americans possess the natural ability of catching the football. However, there is a small percentage of black receivers who lack the soft and steady "hands" to catch perfect passes. Usually, we use the term "butter fingers" to describe people who have shitty "hands" who drop perfect passes. When an African American have "butter fingers", he is known as a "butter nigger". After all, these Butter Niggers are very rare and we all know that most African Americans make perfect Wide Receivers.
A butter nigger would not be able to catch a pass on a 10 yard cross, even if thrown by Tom Brady/Brett Favre.