Struggling reliever Diaz optioned to Triple-A

Statcast indicates less effective changeup could be culprit of power pitcher's stumbles

Struggling reliever Diaz optioned to Triple-A

CINCINNATI -- The Reds knew there would be some unknown quantities within a bullpen where roles weren't set until after Spring Training. One of them wasn't expected to be power right-hander Jumbo Diaz.

Diaz, who was with the club the previous two seasons, was optioned to Triple-A Louisville on Tuesday to make room for starting pitcher Robert Stephenson. Diaz struggled in eight appearances this year, allowing four earned runs on eight hits and three walks. He also gave up three homers, including Ben Paulsen's three-run shot in the eighth inning in Monday's 5-1 loss to the Rockies.

"He's a better pitcher than he's shown in his first eight appearances, we know that," Reds manager Bryan Price said. "But we need the guy we've come to expect to not only be what he's been in the past but exceed that. He needs to be better than he's been at the big league level at this point, and we're confident he can get there. We just can't use the season at this level to help him find his way."

Paulsen's three-run jack

Data provided by Statcast™ indicated a variety of possible reasons that Diaz wasn't effective. It is, of course, a small sample size, as the 32-year-old faced 29 batters this season.

Hitters are certainly missing his stuff less often, as Diaz has a swinging-strike rate of 9.5 percent this month, compared to 15.9 percent in April 2015 and 14.4 percent for all of last season. His swing-and-miss percentage went from 32 percent last season to 20 percent this year.

Opponents were batting .320 against Diaz this season with a .278 average on balls in play -- which shows he's been a little lucky to a degree. Last season, opponents batted .253 with a .322 BABIP while in 2014, he recorded a .230 opponent's average with a .295 BABIP.

The average velocity for Diaz's four-seam fastball was 97.9 mph last season with an average perceived velocity of 98.7 mph. Entering Monday's game, he's averaged 96.2 mph with a perceived velocity of 96.5 mph in 2016. Typical of a chilly April, league-wide velocities are down around 0.5 mph, but that should gradually increase as temperatures rise. Diaz appears to be down over 1.5 mph, however.

Diaz's changeup velocity hasn't declined as much, making for a smaller separation from his fastball. The perceived velocity of the changeup was 90.8 last season and 90.1 this season. Last year, the average separation on perceived velocity between the pitches was 7.9 mph, this year it's 6.4 mph.

When asked about Diaz's velocity, Price didn't view that as a big concern.

"It's pitch execution and pitch usage," Price said. "The thing about pitching in the big leagues is the longer you do it, the more comfortable a pitcher gets pitching at this level, which is a good thing. No. 2 is the other side of that, the league gets more comfortable about what to expect from you as a pitcher, so certainly I'm sure the league is aware that Jumbo throws hard. The key … to his success has to be moving forward the quality of the command because the velocity is no longer overwhelming the hitters. The ability to execute the slider and split-finger with similar quality is the key to his success."

Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, follow him on Twitter @m_sheldon and Facebook and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.