user: Question: what is the sum of totaltk when yards is less than 0?
Columns: ['Player', 'Tackles', 'Asst.', 'TotalTK', 'Sack', 'Yards', 'FumR']
Types: ['text', 'real', 'real', 'real', 'real', 'real', 'real']
Sample row: ['London Fletcher', 96.0, 37.0, 133.0, 0.5, 0.0, 1.0]
SQL:

assistant: SELECT SUM("TotalTK") FROM "Table" WHERE "Yards" < 0.0;