Castillo (4-6) got the loss against the Padres on Sunday, giving up four runs on six hits over 4.2 innings, striking out three and walking one as the Reds eventually fell 6-3.
Castillo had seemed to be putting it together of late after a brutal start to the season, but he's now given up four earned in back-to-back outings, bringing his ERA up to 5.64 and WHIP to 1.45 over 67 innings. Overall, that's a disappointing return so far for a player who was touted as a potential breakout candidate after posting a 3.12 ERA and a 1.07 WHIP with 98 strikeouts over 89.1 innings in his first action at the big-league level last season.