If you go to his game log on b-r.com https://www.baseball-reference.com/players/gl.fcgi?id=rogerta01&t=p&year=2019 and click twice on the DR (days rest) column, this sorts his games with 0 days rest at the top. You can give him a pass for one or two worst outliers, and it's still pretty visible that he's been a different pitcher than his normally spotless self Or, you can sort on the Earned Runs column, and see that in the 11 games where he gave up any, 4 were with rest and 7 were without rest, which is basically the opposite of that ratio when he didn't give up a run. This way of looking at it reduces the impact of one bad game, because you're not looking at averages, but just counting "good game" and "bad game". Last year was a little less extreme, but of the same general pattern. I wouldn't be surprised if this were typical for relievers, and as always with relievers you are right to be wary of Small Sample Size, but I don't think this ought to be ignored.