Blackley, 30, has a 4.89 ERA with 7.5 K/9 and 5.1 BB/9 in 35 innings for Houston this year. The Aussie southpaw has been effective against left-handed hitters, limiting them to a .200/.258/.367 batting line through 66 plate appearances. However, Blackley has yielded a .265/.400/.603 batting line versus opposing righties.
Chapman, 25, has a 3.28 ERA with 10.8 K/9 but a lofty 6.4 BB/9 rate in 50 2/3 innings this season at Oklahoma City. He was acquired from the Royals last season along with outfielder D'Andre Toney in a trade that sent Humberto Quintero and Jason Bourgeois to Kansas City.