Although relievers are hard to track with smaller sample sizes, Graterol is a great example of the eye test and stat sheet combining to state the obvious. Through April 8 (four appearances), Graterol had a 6.75 ERA (3 ER in 4 IP) with only 2 K.
But after an appearance against Arizona when he gave up two earned runs in an inning of relief work, Graterol put up zero after zero through the end of April. By the end of April, Graterol had a 2.19 ERA with 2 saves and 2 holds (including a dramatic two-inning save against the Cubs), thanks to nine straight outings (8.1 IP) without allowing a run.
Even after giving up a run to the Phillies and the Padres, Graterol bounced back against the Brewers, pitching a scoreless inning with a pair of strikeouts. He has more than halved his ERA since April 8, and looks to be trending in the right direction for the rest of the season. If Graterol keeps performing like he has recently, he will likely solidify the eighth-inning role for the Dodgers, occasionally closing games when Evan Phillips is unavailable.
Of course, he needs to stay healthy to seize the role, which has been an issue throughout his career.