Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What is the average round when there is a defensive back and an overall smaller than 199?

### Inputs:
table_name: table, columns: ['Round', 'Overall', 'Player', 'Position', 'School/Club Team']

### Response:
SELECT AVG Round FROM table WHERE Position = defensive back AND Overall < 199