[Flashlight]

...Obviously there aren't many people, at least in major sports, who have won an MVP in their rookie season...

That's what I was thinking, but read the question again. The athlete won a "championship", not an "award." I'm thinking that "championship" refers to a team world champion (not Western division championship, for example), and not a "statistics" champion, like a "batting championship."

Also, the guy could have had a short carreer of three years and still fulfill the requirements.

[Flashlight]

okay, he played 7 years, my mistake...

[Mr. Mulliner]

Bob Feller won a championship in his last year, but doubt he won his rookie year with the Indians.