I don't pretend to know much of anything about sabermetrics, but I took a look at Brock's defensive stats on baseballreference.com anyway. http://www.baseball-reference.com/players/b/brocklo01-field.shtml Seems to me there are a lot of negative numbers there. If I'm reading it right, he was a below average defensive outfielder. He was almost exclusively a left fielder when he got to St. Louis. My understanding is that in professional baseball, you "hide" your worst defensive outfielder in Left. So, given that he had to play left field, just exactly where was he going to play for the Cubs? He certainly wasn't going to take Billy Williams' place.