Byrd will serve as a replacement for Hunter Pence, who is back on the disabled list with an oblique strain. Byrd joins Norichika Aoki as options in left field for the Giants, with Gregor Blanco and Justin Maxwell rounding out a weakened outfield mix.
Byrd was a trade candidate in advance of the non-waiver trade deadline in July, but stayed put in Cincinnati while teammates Johnny Cueto and Mike Leake were traded. The 37-year old has hit just .237/.286/.448 with nineteen homers in his first season as a Red, and is controllable for next season as a result of a team option that will become available if he does not hit 550 plate appearances by the end of the year. The Giants are Byrd's ninth major-league team, joining the Phillies, Nationals, Rangers, Cubs, Red Sox, Mets, Pirates and Reds.
Johnson, 24, was the Giants' sixth-round pick in the 2012 draft, and has posted a 3.41 ERA in 58 relief innings for Double-A Richmond so far this season. He did not rank as one of the Giants' top thirty prospects at the time of the trade.