Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_49 (round INTEGER, position VARCHAR, overall VARCHAR)

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

### Accurate SQL ###

SELECT AVG(round) FROM table_name_49 WHERE position = "defensive back" AND overall < 199