Marble greatly contributed to the desegregation of American tennis by writing an editorial in support of Althea Gibson for the July 1, 1950 issue of "American Lawn Tennis Magazine". The article read "Miss Gibson is over a very cunningly wrought barrel, and I can only hope to loosen a few of its staves with one lone opinion. If tennis is a game for ladies and gentlemen, it's also time we acted a little more like gentle-people and less like sanctimonious hypocrites...If Althea Gibson represents a challenge to the present crop of women players, it's only fair that they should meet that challenge on the courts." Marble said that, if Gibson were not given the opportunity to compete, "then there is an ineradicable mark against a game to which I have devoted most of my life, and I would be bitterly ashamed." Gibson, age 23, was given entry into the 1950 U.S. Championships, becoming the first African-American player, man or woman, to compete in a Grand Slam event.