The road was a bit rocky for Diaz in 2017, with the Mariners temporarily relieving him of closer duties on a couple occasions, but when it was all said and done Diaz tied for fourth in the American League in saves. He converted 21 of 23 save opportunities in the second half and struck out 32 percent of the batters he faced overall using a combination of high-90s fastballs and high-80s sliders. Diaz can be his own worst enemy with the walks, and the uptick in home runs last season is a concern, although he was better in that regard down the stretch (two homers allowed in his final 30.1 innings). His stuff is electric most of the time and there aren't any proven options behind him in the Seattle bullpen, so Diaz should be given every chance to remain in the closer role throughout 2018. However, he's not exactly a "safe" investment given the slip in performance from 2016 and the general year-to-year unpredictability of major-league relievers.