The Cubs acquired Russell plus Minor League pitcher Dan Straily, outfielder Billy McKinney and a player to be named later from the Athletics for starting pitchers Jeff Samardzija and Jason Hammel.
When the Cubs selected Baez in the first round of the First-Year Player Draft in 2011, the question was, what happens to Castro? The response came in August 2012 when Epstein signed Castro to a seven-year, $60 million contract.
Who's the odd man out?
"The nice thing about having impact players who are athletic and can play in the middle of the field and can hit is that you have options," Epstein said on Saturday. "You can never have too many shortstops. If you look around baseball, you see some of the best outfielders in the game came up as shortstops, some of the best third basemen in the game came up as shortstops, some of the best second basemen in the game came up as shortstops. Heck, some of the best first basemen in the game came up as shortstops."
Epstein said Baez can play second, third and the outfield if needed, and Russell can play anywhere in the infield. Two other middle infielders at Iowa, third baseman Kris Bryant and Arismendy Alcantara, also can play in the outfield. Expect to see Baez start at other positions in the second half.
"The good thing is these guys can all fit on the field together and be a really impactful team together because of their athleticism and versatility," Epstein said.
Baez has played strictly at shortstop, and Russell will be joining Double-A Tennessee, so there won't be a logjam at Iowa. Russell, 20, has "tremendous instincts, tremendous hands," Epstein said, and has shown good discipline at the plate. He played with Bryant on the left side of the infield in the Arizona Fall League last October.
"We're excited about his future," Epstein said of Russell.
Castro is only 24, but this is his fifth season in the big leagues. He's bounced back from a .245 season last year, and was batting .290 entering Saturday with more home runs and RBIs prior to the All-Star break than he totaled in 161 games in 2013.
Should Castro be a little nervous with the young shortstops now in the mix? Epstein called Castro's agent to assure him not to worry, but the addition of Russell does give the Cubs depth at a valuable position.
"We're proud of [Castro]," Epstein said. "It's not easy to bounce back from the year he had last year and he's bounced back in a big way and playing at an elite level. He's a centerpiece-type guy for this organization."
And somehow there is room for everyone.