As Hans Schlesinger in Germany, he was a top field hockey goalie in the 1930s for Germany. But as a Jew, the Nuremburg Laws made it increasingly difficult for him to compete in sports. He left the country in 1935 and got a job at Bear Stearns investment bank, where he worked as a runner for stock trades, and took the name John Slade. He moved up quickly at Bear Stearns and eventually became a partner in the firm in 1951. He served for the US Army in World War II, interrogating German prisoners-of-war and was awarded a Bronze Star for his service. He continued to compete in hockey and was able to represent the United States in London in 1948, which he called one of the signal events of his life.