Last night, Shelby Miller turned in a performance worth -80.2% of win probability. It wasn’t quite the worst of the year for Arizona - Miller himself rated -80.9% in an extra-inning loss to the Dodgers on May 20. But it did drop the Diamondbacks’ bullpen as a collective entity into dead-last place in the majors this year, for Win Probability by relievers. All told, they have been worth -291%. Only three other teams - the Athletics, White Sox and Nationals - are even below zero in this metric. [This is normal: by the nature of the metric, pitching typically is well above zero, while hitting is well below it, because an out - success for a pitcher, failure for a hitter - is the most likely outcome]
If you break it down to the individual level, you can see who is responsible.