Jackie Robinson signed with the Brooklyn Dodgers ' organization on Oct. 28 , 1945 , spent spring training in Daytona Beach , Fla. , with the Montreal Royals of the International League and on April 18 , 1946 , he was the Royals ' second baseman in Jersey City where Mayor Frank Hague 's political clout had created an opening-day sellout crowd of 25,000 in Roosevelt Stadium .