3. Marcus Stroman
Marcus Stroman wound up returning early from his rare rib cartilage injury, but his performances so far haven't been game changing. Manager Davis Ross even restored Stroman's starting duties only to see the 32-year-old struggle to get through three innings in each of his two starts.
Perhaps this entry is more of an indictment on Ross, who foolishly transitioned Javier Assad back to the bullpen when he had been excelling as a starter for the last two months. It would have made more sense to keep Assad where he was and use Stroman as a piggyback since he is probably on a limited work load anyway coming back from injury. Admittedly, Assad struggled in a road start against the Rockies, but he bounced back in his next game against the Pirates.
This is just one of many examples of Ross prioritizing veterans over rookies who were performing well. But this decision could be one that costs the Cubs a playoff appearance.