The wordplay takes alternate letters of Ashe (with the regular ones missed out) leaving AH, which is then placed inside WOO (court, as in to woo someone) to give W-AH-OO. The 1 is a cross-reference to 1 down (FISH), defining the wahoo as a type of fish — with 'No.' just smoothing the surface to evoke tennis player Arthur Ashe on Court No. 1.