Conversation so far:
When did Imran Khan become a captain?
in 1982
Where was Imran Khan a student?
Imran Khan was educated at Aitchison College in Lahore, then the Royal Grammar School Worcester in Worcester, and later at Keble College, Oxford
What was Imran Khan a captain of?
the Pakistan cricket team

Question: When was he a captain there?
Self-contained rewrite: When was Imran Khan a captain for the pakistan cricket team?