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_6387 ( "Rank" real, "Name" text, "Attempts" real, "Net Yds" real, "Yds/Att" real, "Touchdowns" real, "Long" real, "Start" real )

### Question ###
What is the average net yds for the player who had a long of 68 and started after 1984?

### Accurate SQL ###

SELECT AVG("Net Yds") FROM table_6387 WHERE "Long" = '68' AND "Start" > '1984'