Although most of the spring fervor has centered on Cuban lefty Aroldis Chapman, the right-handed Del Rosario's abilities have sparked much buzz around Reds camp.
"He's impressed me," Reds manager Dusty Baker said. "You wouldn't know it's his first time in big league camp. He fields his position well. I talked to some guys about him and they said he calls infielders off. He's such a great fielder. He keeps the ball down, runs it in on them. There's always a place on a team, sooner or later, for a guy with a good natural sinker."
Del Rosario speaks little English but when asked through a translator what turned his career around, two words were clear.
"Tom Brown," Del Rosario said.
Last season, Del Rosario posted a 3-1 record and 1.68 ERA with 12 walks and 54 strikeouts in 50 games combined at three levels. He zoomed all the way from the Florida State League to Triple-A Louisville and was added to the 40-man roster. The previous season where he was used as a starter and reliever, he had a 6.09 ERA in 13 games for Sarasota after a promotion from Class A Dayton.
It took a change of arm angle for things to get back on track. Del Rosario, now 24, went from throwing overhand to becoming a sidearm thrower with a nasty sinker.
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"I hoped I could help him a little bit," Brown said. "He was just one of those guys that had an over-the-top four-seam fastball and threw 93 mph. He had a 9.00 ERA and that didn't work real well. But he was such a great athlete. He had the ability to field his position, make quick decisions and do things almost like a shortstop.
"[Then Gulf Coast League Reds manager] Pat Kelly and I sat there and said you know what? Let's give it a shot."
The process of changing Del Rosario's arm angle was gradual. First, he went from overhand to three-quarters side arm and now he's at what could be considered lower three-quarters. At Sarasota, catchers Devin Mesoraco and Jake Long led him through the game and reminded Del Rosario between pitches to "change his slot" if he slipped back to overhand.
"I threw much better and I feel much better from the side than overhand," said Del Rosario, who worked one perfect inning during Monday's "B" game vs. the Brewers. "I was throwing too straight and the hitters got me pretty good. From the side, I got more sink and more movement."
"He started to figure it out and realized how good of a sinker he has," Brown said. "He understood this is all I have to do. It's not like he had to overpower guys anymore. He could get a ground ball and being the great athlete he is, you can't bunt on him."
Upward mobility came quickly after Del Rosario spent the first half the season in Sarasota. There were just 10 days logged at Double-A before a promotion to Triple-A on July 30.
In 15 games for Louisville, Del Rosario posted a 1.09 ERA and the ERA was 1.99 over 22 1/3 innings for Cibao of the Dominican Winter League.
With Del Rosario's sinker, an improved slider and ability to throw strikes, the Reds envision his eventually being a late-innings reliever. With runners on base, he could induce double plays and get his team out of tight situations.
"He has confidence in what he does," Brown said. "He's got a great pickoff move. He's a great PFP guy. You can't bunt on him. He can turn double plays on ground balls other pitchers couldn't get to. Ernie is not afraid. It takes a special guy to pitch late in the game, it really does. It's not just stuff. It takes a special makeup. Ernie has no fear. If he gets beat today, he will beat you tomorrow."