The ever-active Baltimore Orioles promoted rookie lefty Jayson Aquino to the major league roster on July 4th. He made his debut in relief with two-thirds of an inning against the Los Angeles Dodgers and more chances will come. Let's take a look at what he offers.
Aquino has been playing roster jump for the last 18 months, most recently being sold by the Cardinals to the Orioles this past spring training. This comment from the 2016 Baseball Prospect Book was written before he joined the Orioles but lays out the basic background.
Jayson Aquino, LHP, St. Louis Cardinals
Bats: L Throws: L HT: 6-1 WT: 170 DOB: November 22, 1992
2013: Grade C+; 2015: Grade C: 2015: Grade C
Jayson Aquino was an interesting prospect in the Rockies system three years ago, but difficult 2013 and 2014 seasons cut into his stock. He was traded to the Blue Jays in February 2015, then was traded to the Pirates in May 2015, then was sold to the Indians in July 2015. He’s with the Cardinals now, claimed on waivers in December. They like him enough to give him a spot on the 40-man. All the roster shuffling obscures the fact that he pitched quite well last year, posting a 3.28 ERA with an 86/30 K/BB in 137 innings with a 2.16 GO/AO. Aquino has an 88-92 MPH sinker but his curve and change-up are solid and he usually throws strikes. He’s a fifth starter or bullpen type but for some reason I’ve always felt he could take a leap forward at some point. 2015 was a step in that direction but it hasn’t happened yet. Grade C.
The Orioles were using Aquino as a starter for Double-A Bowie, where he posted a 3.25 ERA in 80 innings with a 55/22 K/BB and 1.55 GO/AO. This was similar to what he did in the Blue Jays and Pirates systems last year.
Although he started for Bowie the general consensus projects Aquino as more of a reliever at higher levels. He doesn't necessarily throw harder in shorter doses (he topped out at 90 against the Dodgers) but he's less likely to get overexposed in that role. The Orioles used him as a LOOGY in his debut, coming in to pitch against Corey Seager and Chase Utley. That would seem to be the best theoretical use for Aquino, but in fact he's shown reverse platoon splits the last two years. Make of that what you will.
As a lefty with a decent arm and track record, Aquino will be in the bullpen picture somewhere for the next few years. He's hasn't yet taken a huge leap forward, but southpaws with pulses get many opportunities and he's still just 23.