This isn't a topic that requires much elaboration at this point, but the Pirates should make someone else their closer and remove Jason Grilli from high-leverage situations completely until he shows he's capable of handling them again.
Last night's home run to Todd Frazier -- on a terrible fastball, and coming in an outing in which Grilli struggled to throw strikes -- wasn't Grilli's first big mistake this year. There was also the terrible three-walk outing in Miami and a bad outing against the Dodgers. And that's just in the last two and a half weeks. For the season, Grilli has walked 10 batters in 17.2 innings, and his strikeout rate, while fine overall, is way off where it was last year. Neither his fastball nor his slider are as effective as they've been in the past.
I'm sure Mark Melancon would take Grilli's place if the Bucs were to replace him, but who exactly pitches the ninth doesn't matter so much. What matters is that it isn't Grilli, at least not right now. We've had discussions in the past about how it's okay to have your second-best reliever close because closers don't always pitch high-leverage innings anyway, but Grilli isn't the Pirates' second-best reliever. Tony Watson, Melancon, and Justin Wilson have all clearly been better. Heck, even Jared Hughes and Jeanmar Gomez have been better. And if the Pirates somehow end up contending, they should be looking for bullpen help (which, fortunately, isn't that hard to find). For now, the Bucs need to let Grilli pitch garbage time -- perhaps for only a few outings, but long enough to show he's still capable of reminding us of 2013-vintage Jason Grilli, rather than 2008-vintage Tyler Yates.
EDIT (from David): As usual Charlie beat me to this, but I added my two cents with some numbers on Grilli over on my station blog.