One of the biggest moments between the two clubs off the field happened on August 6, 2004, when the Rockies sent Larry Walker to the Cardinals in exchange for Jason Burch and two players to be named later. Walker would go on to play with the Cardinals in the 2004 World Series against the Boston Red Sox. In the Fall Classic, Walker would post a .357/.438/.929 with a 1.366 OPS as the Red Sox swept the series.
Walker would play 100 games for the Cardinals the next season before retiring.
That was the second-ever trade between Colorado and St. Louis. The first came on November 16, 1999, when the Rockies traded Luther Hackman, Darryl Kile, and Dave Veres to the Cardinals for Manny Aybar, Brent Butler, Rich Croushore, and Jose Jimenez.
Among the players who have played for both franchises include Royce Clayton (1996-98 Cardinals and 2004 Rockies), Dexter Fowler (2008-2013 Rockies and 2017-19 Cardinals), Andres Galarraga (1992 Cardinals and 1993-97 Rockies), and Matt Holliday (two stints with Rockies and 2009-16 Cardinals).