The term 'Say Hey Kid of Baseball' is a reference to the legendary baseball player Willie Mays, who was known for his signature phrase 'Say Hey'. Mays was a Hall of Fame center fielder who played for the New York and San Francisco Giants and the New York Mets from 1951 to 1973. He was an All-Star for 20 seasons and won two MVP awards. He was also known for his incredible defensive skills, earning him the nickname 'The Say Hey Kid'.