For Aro, 24, this is his third career major league stint, all this season. All three of his appearances with Boston came during his first big league stretch from June 25-July 1, over which he allowed six runs in 4.2 innings (11.57 ERA) with three strikeouts. In 31 minor league appearances between Double-A Portland and Pawtucket this season, the right-hander is 3-3 with two saves, a 3.06 ERA (23 ER), and 69 strikeouts in 67.2 innings, holding opponents to a .212 batting average (53-for-250) while allowing just 16 walks. In 23 games since being promoted to the PawSox in mid-May, the Dominican native has totaled 50 strikeouts and just 10 walks in 45.1 innings, posting a 3.18 ERA (16 ER). Signed by Boston as an international free agent in June 2011, Aro has gone 16-15 with 13 saves, a 2.84 ERA (93 ER/295.0 IP), and 288 strikeouts in 98 outings (12 starts) over parts of five minor league seasons in the Red Sox system.
Barnes, 25, started last night's loss to the Royals at Fenway Park, allowing five runs in 5.1 innings. It was his second career major league start, both in his most recent big league stint. In 23 overall major league outings this season, the right-hander is 3-4 with a 6.89 ERA (25 ER/32.2 IP) and 31 strikeouts. With the PawSox this year, the Connecticut native has gone 1-1 with a 4.17 ERA (17 ER), striking out 39 batters in 36.2 innings over 16 outings (5 starts). Barnes, who made his big league debut with five relief outings for the Red Sox last season, is 3-4 with a 6.26 ERA (25 ER/32.2 IP) in his major league career with 39 strikeouts and only 14 walks. Signed by the Red Sox as a first-round selection in the 2011 June Draft, he is 22-25 with a 3.69 ERA (163 ER) and 417 strikeouts in 397.1 innings pitched over 89 career minor league outings (77 starts) from 2012-15.