Cashner, a former first-round pick of the Cubs, has made 59 of his 60 Major League appearances out of the bullpen since debuting in 2010. He has gone 2-6 with a 4.29 ERA (31 ER/65.0 IP), averaging 8.0 strikeouts per 9.0 IP along with a .241 opponent average. The 25-year-old missed the majority of the 2011 season after suffering a strained rotator cuff in his right shoulder in April. He made one start prior to sustaining the injury, returning in September to make six relief appearances. He finished 2011 with a 1.69 ERA (2 ER/10.2 IP), allowing just three hits and four walks while striking out eight.
Signed as the 19th overall pick by the Cubs in the 2008 First-Year Player Draft out of Texas Christian University, Cashner was also selected in the 2005, 2006 and 2007 drafts but did not sign. Over his 48 minor league appearances (42 starts), he has gone 10-8 with a 2.82 ERA (72 ER/182.0 IP), 161 strikeouts and just three home runs allowed.
Na, who turned 20 in December, was signed by the Cubs as a non-drafted free agent on August 12, 2009. A native of Seoul, South Korea, Na has spent two seasons in the Cubs minor league system. In 149 minor league games, he has hit .244 (109-for-447) with 14 doubles, two triples, 33 RBI, 64 runs scored and 26 stolen bases.
Rizzo, 22, spent one year in the Padres organization after being acquired on December 6, 2010. He spent the majority of 2011 at Triple-A Tucson, where he hit .331 (118-for-356) with 34 doubles, one triple, 26 home runs, 101 RBI and 64 runs scored in 93 games. Rizzo made his Big League debut with the Padres last year, and hit .141 (18-for-128) with eight doubles, one triple, one home run, nine RBI and nine runs scored in 49 games.
Over parts of five minor league seasons in the Red Sox and Padres organization, Rizzo has hit .296 (425-for-1436) with 119 doubles, one triple, 64 home runs, 281 RBI and 234 runs scored in 278 games.
Cates, 22, was signed by the Padres as a third-round selection in the 2010 Draft and made his professional debut with Single-A Fort Wayne in 2011. He went 4-10 for the TinCaps, posting a 4.73 ERA (62 ER/118.0 IP) in 25 starts.