Task: Explanation
Input (English): The 1999–2000 NBA season was the 11th season for the Orlando Magic in the National Basketball Association. During the offseason, the Magic hired Doc Rivers as Head Coach while acquiring Tariq Abdul-Wahad from the Sacramento Kings, Chris Gatling from the Milwaukee Bucks, Ben Wallace from the Washington Wizards, second-year forward Pat Garrity from the Phoenix Suns, and rookie Corey Maggette from the Seattle SuperSonics, while signing free agents John Amaechi and Monty Williams. The Magic's transition continued at midseason, trading Abdul-Wahad and Gatling to the Denver Nuggets for Ron Mercer, Chauncey Billups and Johnny Taylor. However, Billups never played for the Magic due to a shoulder injury he sustained in Denver. Question: Who was the head coach during the 1999 season in which Ben Wallace was traded from the Washington Wizards? Answer: Doc Rivers
Output (English):  During the offseason, the Magic hired Doc Rivers as Head Coach while acquiring Tariq AbdulWahad from the Sacramento Kings, Chris Gatling from the Milwaukee Bucks, Ben Wallace from the Washington Wizards, secondyear forward Pat Garrity from the Phoenix Suns, and rookie Corey Maggette from the Seattle SuperSonics, while signing free agents John Amaechi and Monty Williams.