user: Question: What is the average round when there is a defensive back and an overall smaller than 199?
Columns: ['Round', 'Overall', 'Player', 'Position', 'School/Club Team']
Types: ['real', 'real', 'text', 'text', 'text']
Sample row: [2.0, 40.0, 'Billy Corbett', 'Offensive Tackle', 'Johnson C. Smith']
SQL:

assistant: SELECT AVG("Round") FROM "Table" WHERE "Position" = 'defensive back' AND "Overall" < 199.0;