Answer:
Credibility and an American approach to sports analysis.
Explanation:
The biggest difference in sports analysis between Europe and America is, in many's view, the Americans' obsession with statistics. One cannot watch a sports game without the commentators using at least a dozen statistics to prove the greatness/importance of a team, player or game.
Gerald Early is no different. The task of writing about Jackie Robinson is not easy for anyone, with Robinson being such an important figure in American sports. Early was probably not the first and surely will not be the last to do that.
In order to add credibility to his writing, distinguish his work from those of other people and last, but not least, to appeal to the American reader, Early tries to use as many sources as possible to support his arguments. He does that masterfully because, instead of the sources diminishing Early's voice in the writing, they do the opposite. Gerald Early uses the sources to enhance his own voice by always making the sources' relevance dependent on his own claims.