This is similar to a couple of posts that I did last April. See Who Was The Least Likely Triple Crown Winner? and Baseball's Elite, Its Millionaires. In those posts I used all of a player's career stats to determine the rankings (Ruth was the most likely to do it among the guys who never did). Here I looked at each guy who won the triple crown but his rating was based only on what he did before his triple crown season. For Williams and Hornsby, I used their first time (I also only looked at guys since 1900 this time).
A player would get 10 points for each time he led his league in HRs, 9 for a 2nd place, etc. The same was done for AVG and RBIs. So the player had a career total number of points for each stat. A tie for 1st was still worth 10 points. Then those three numbers were multiplied times each other (meaning if a player never finished in the top 10 in one of these stats, his total will be zero).
So Yastrzemski was the most surprising. He did not make the top 10 in either HRs or RBIs in his six seasons before he won the triple crown (he was also the least likely to win using career data since 1900).
Cabrerra would not be that big of a surprise, especially considering that he has led the league in all three stats in different years already. Gehrig was not a surprise at all he had been in the league leaders for several years in all three stats many times. Maybe his age of 31 made it a little more surprising. But it is not like his career was in decline before that.