Conversation so far:
When did Roger Clemens join the Red Sox?
Roger Clemens was drafted 19th overall by the Boston Red Sox in 1983
How did Roger Clemens perform in his first season on the Red Sox?
Roger Clemens quickly rose through the minor league system, making his major league debut on May 15, 1984.
How much was Roger Clemens paid by the Red Sox?
How long was Clemens on the Red Sox?
Roger Clemens was on the Red Sox for 12 years
What team did Roger Clemens join after the Red Sox?
Roger Clemens left and signed with the Toronto Blue Jays.

Question: Why did he leave the Red Sox?
Self-contained rewrite: Why did Roger Clemens leave the Red Sox?