a member of the orioles' fabled "kiddie corps" of young pitchers signed in the late 1950s (others included milt pappas, steve barber and chuck estrada), walker is one of a very few players to have gone straight to the major leagues without ever playing a game in the minor leagues. in his debut, on july 6, 1957, against the boston red sox, he failed to retire a batter, issuing bases on balls to mickey vernon and jackie jensen, then uncorking a wild pitch. walker then was lifted from the game, but both runners scored, giving walker an earned run average of infinity coming out of his first mlb game. however, he was consistently more effective as the season progressed, and threw a four-hit, complete game shutout against the washington senators on september 4, beating camilo pascual 1–0 for his first big-league victory.