James Russel has worn many hats this year. The hat of a starter, the hat of a reliever, probably some other hats.
He has started 5 games, all of which were Cubs losses, all of which he got the decision for. Overall in these 5 starts 18.1 IP, 19 ER, 5W and 10K. That's over a 9 ERA.
Take that away though, and Russel has 24.1 IP and only 5 ER out of the bullpen. 5W and 18K to go along with it. That's an ERA of 1.8!!! He has a 1-0 record during that time.
It's not surprising that he has large splits. He's very good against lefties with a 1.08 whip but terrible against righties with a 1.62 whip. (ERA is not available for L/R splits because a run is a combination of several hitters. In the bullpen he can be used selectively against more lefties.
Going forward, let's not use Russel as a starter. Not only is it an instant loss, but he takes him away as a bullpen option.