Drew Smyly was removed from the rotation following a disastrous start against the Mets earlier in the month, his fourth in a row allowing at least four earned runs. He made two quasi-relief appearances in there as well, working as the bulk man with mixed results. The Cubs were able to shorten the rotation because they had three off days in just over a week between the Mets and Royals, which gave David Ross an opportunity to get Smyly right with bullpen duty.
The experiment appears to have worked in a very limited sample, with Smyly tossing scoreless innings in three appearances.