Conversation so far:
What year did Bobby Orr retire?
Bobby Orr retired in 1978 at age 30.
What was Bobby Orr doing for work at time of retirement?
At the time of retirement, Bobby Orr was a player for the Chicago Black Hawks.
What was Bobby Orr doing with Chicago?
Bobby Orr was Defenseman for the Black Hawks.

Question: Why could he no longer play?
Self-contained rewrite: Why could Bobby Orr no longer play?