Day, who started tennis at the age of eight, prefers the clay court.
At the Connecticut Open in New Haven , she played as a lucky loser in the main draw of a WTA tournament for the first time in 2016 . There she lost in the first round with 0: 6 and 3: 6 against Ana Konjuh . By winning the Girls' 18s National Championships , she received a wildcard for the main draw in the women's singles at the US Open , where she was eliminated in round two. She won the junior title, in the final she defeated Viktória Kužmová 6: 3 and 6: 2.