In 1961 – the season a 1962 card would have recognized – Maris set a Major League record by hitting 61 home runs, a record that still stood when the episode aired in 1990. According to the Star Trek Encyclopedia (4th ed., vol. 2, p. 21), the previous record holder was Babe Ruth.
According to the Encyclopedia (4th ed., vol. 2, p. 21), the birth and death years of Roger Maris were 1934 and 1989, respectively.