The Giants had to protect Brown on the roster or risk losing him in next month's Rule 5 Draft. Players initially signed at age 19 or older must be added to 40-man rosters within four seasons, or they become eligible to be taken by other organizations through the Rule 5 process. Brown was 21 when the Giants signed him.
Brown has regressed statistically while advancing one Minor League classification annually. Since batting .336 with Class A San Jose in 2011, Brown finished at .279 at Double-A Richmond the following year and .231 at Triple-A Fresno last season. Brown prompted concern within the organization by hitting just .221 off right-handers in 2013.
The Giants also added third baseman Adam Duvall and right-handers Kendry Flores and Hunter Strickland to the 40-man roster.
Currently playing for Bravos de Margarita in the Venezuelan Winter League, Duvall batted .252 with 17 home runs and 58 RBIs for Richmond this year. Duvall, 25, was a non-roster invitee to big league Spring Training camp in 2013 and has hit 73 homers in three and a half Minor League seasons.
Flores, who turns 22 on Sunday, finished 10-6 in 22 starts with a 2.73 ERA, fifth-best in the South Atlantic League, for Class A Augusta. Opponents batted just .216 off him.
After the Giants claimed Strickland off waivers in April from the Pittsburgh Pirates organization, he posted a 1-0 record with nine saves and a 0.86 ERA in 20 appearances for Class A San Jose. Strickland's season ended in late May when he underwent Tommy John elbow surgery.
Moscoso, 30, was 2-2 with a 5.10 ERA in 13 appearances for the Giants, including two starts, after being acquired from the Cubs on July 26.
Chris Haft is a reporter for MLB.com. Read his blog, Haft-Baked Ideas, and follow him on Twitter at @sfgiantsbeat. This story was not subject to the approval of Major League Baseball or its clubs.