Executive Vice President/General Manager Ben Cherington made the announcement.
For the 24-year-old Aro (pronounced "AH-row"), this is his first career major league stint. In 18 appearances this season, all in relief between Double-A Portland and Pawtucket, the right-hander is 3-2 with one save, a 2.22 ERA (11 ER) and 49 strikeouts in 44.2 innings. The Dominican native, who last pitched on June 22, has held opponents to a .184 batting average (30-for-163) while allowing just 11 walks. In 10 games since being promoted to the PawSox on May 14, he has 30 strikeouts and just three walks allowed in 22.1 innings, posting a 1.61 ERA (1 ER). He is currently amidst an 18.0-inning scoreless streak over his last eight appearances with the PawSox. Signed by Boston as an international free agent in June 2011, Aro has gone 16-14 with 12 saves, a 2.68 ERA (81 ER/272.0 IP) and 268 strikeouts in 85 outings (12 starts) over parts of five minor league seasons in the Red Sox system. Prior to this season, he had never pitched above Single-A, spending most of 2014 with Greenville, where he was named a mid-season South Atlantic League All-Star.
Bradley, 25, is beginning his third major league stint of the season. The outfielder has appeared in seven games, all Red Sox victories, and played all three outfield positions for Boston this season, making two starts in right field and one in center field. Bradley has hit .322 (66-for-205) with 26 runs, 18 doubles, four home runs, and 16 RBI for Pawtucket, ranking second in the International League in batting average and on-base percentage (.398), as well as tied for fifth in doubles. He has recorded five outfield assists in 51 minor league games this season, making 49 starts in center field and two in right field. In 170 career major league games, Bradley has hit .192 (94-for-490) with 63 runs scored, 24 doubles, two triples, four home runs, and 40 RBI.
Marrero, 24, is also beginning his first career major league stint. The right-handed batter has played the entire 2015 season with Pawtucket, batting .241 (56-for-232) with 10 doubles, one triple, four homers, 21 RBI, 30 runs, 19 waks, and nine stolen bases in 66 games. Defensively, he has appeared in 60 games this year at shortstop, five at second base, and one at third base. The native of Miami, FL entered the season as Boston's No. 9 prospect according to Baseball America. He was tabbed the Red Sox 2014 Minor League Defensive Player of the Year after posting a .976 fielding percentage between Portland and Pawtucket, and was named the organization's 2013 Minor League Base Stealer of the Year after succeeding in a minor league-leading 27 of 29 stolen base attempts (93.1%). A first-round selection (24th overall) by the Red Sox in the 2012 June Draft, Marrero has hit .256 (341-for-1,332) with 72 doubles, six triples, 14 homers, 129 RBI, and 76 stolen bases over parts of four minor league seasons.
Pedroia, 31, has hit a team-best .306 (86-for-281) with 34 runs, 14 doubles, nine home runs, and 33 RBI in 69 games. In his 10th major league season, the second baseman ranks among American League leaders in hits (T-4th), batting average (7th), and multi-hit games (T-6th, 25), also ranking second in the majors with a .361 batting average at home. He batted leadoff in 24 consecutive games from May 23 to June 17, during which he shared the American League lead in hits (35) and ranked fourth in batting average (.350). The right-handed batter is a career .300 hitter (1,457-for-4,861) with 334 doubles, 13 triples, 115 home runs, and 579 RBI in 1,220 career games with the Red Sox since 2006. He recorded his 1,455th career hit on June 21, moving into 10th place on the Red Sox' all-time hits list.
Kelly, 27, is in his first full season with the Red Sox after being acquired in a trade with the St. Louis Cardinals on July 31, 2014. In 14 starts for Boston this year, the right-hander has gone 2-5 with a 5.67 ERA (47 ER/74.2 IP), while also averaging a career-high 7.2 strikeouts per innings pitched (60 SO). For his major league career, Kelly has a 23-21 record and 3.83 ERA (171 ER/402.0 IP) with 280 strikeouts in 92 games (62 starts) between the Cardinals (2012-14) and Red Sox (2014-15).
Kratz, 35, was claimed off waivers from the Royals on Sunday and did not appear in a game for the Red Sox. He had been designated for assignment by Kansas City on June 11 following a stint on the 15-day disabled list due to plantar fasciitis. The right-handed batter appeared in four major league games this season, making one start. At the plate, he was hitless in four at-bats with one RBI on a sacrifice fly. In 15 games for Triple-A Omaha this season, he batted .214 (12-for-62) with seven runs, two doubles, four homers, 12 RBI, and five walks. A veteran of parts of six major league seasons with the Pittsburgh Pirates (2010), Philadelphia Phillies (2011-13), Toronto Blue Jays (2014), and Royals (2014-15), Kratz is a career .217 (107-for-492) hitter with 21 doubles, 23 homers, 67 RBI, and 35 walks in 180 games. The native of Harrisonburg, VA was originally signed as a 29th round selection in the 2002 June Draft by the Blue Jays.
With these moves, the Red Sox 40-man roster is now full.