This is Diaz's third time being on the big league roster this season; he began the year with the Reds and made eight appearances before being optioned to Louisville on April 19 with a 5.40 ERA. He was previously recalled on May 18 and made three more relief appearances, allowing three earned runs on two hits with four walks and two strikeouts in 3 1/3 innings, before again being sent to Louisville on May 22.
Diaz's numbers in Triple-A have been outstanding. In 22 appearances for the Bats, he's 1-1 with a 0.75 ERA and 11 saves in 24 innings. He's walked just seven batters and given up 16 hits -- none of them home runs -- while striking out 28 batters.
The trick for Diaz will be to find a way to transfer that success to the Major League level. In his 11 appearances for the Reds this season, covering 10 innings, he's allowed 10 hits, half of which have been home runs. He's also walked seven while striking out just six.
"He's got to come out and perform," Reds manager Bryan Price said. "You have to be good each at-bat, each pitch. Bridging that gap is challenging for anybody. I'd love to see him pitch in similar fashion as he was in Triple-A. But who wouldn't? Those are really good numbers."
It's not as if Diaz has not had success in the Majors before. He appeared in 36 games in 2014 when he made his Major League debut at the age of 30 after spending more than 12 seasons in the Minors. He struck out 37 batters in 34 2/3 innings that season while accumulating a 3.38 ERA. After a rough start to the 2015 season resulted in him being sent to Louisville the first week of June, Diaz was recalled on July 17 and posted a 2.65 ERA in 36 appearances through the remainder of the season.
Diaz will be used in a middle relief role. The return of Michael Lorenzen and Raisel Iglesias to the bullpen means Price won't be using Diaz in many late-inning situations.
"I'm not terribly reluctant to use Lorenzen or Iglesias later in the game," said Price. "There will be a lot more opportunities in the middle innings for Jumbo than in the back end when we're ahead or it's close."
Reliever Caleb Cotham, who has been on the disabled list since May 31 with inflammation in his right shoulder, threw 20 pitches of live batting practice Monday as part of an overall hour-long throwing session. The Reds are hopeful of being able to send Cotham on a rehab assignment after this homestand ends on Wednesday.
"I just wanted to be consistent in the process and in my routine," Cotham said about Monday's session. "It's buying into every pitch and throwing every pitch with conviction, and living with the results."
Cotham has appeared in 23 games this season, allowing 32 hits and 21 runs in 24 1/3 innings.
Depending on how Cotham's shoulder feels in the next couple of days, the Reds will then make the decision on whether he will throw another live BP or bullpen session, or if he's ready to face live competition in the Minors.