On Sept. 6, 2011 Brett Pill made his Major League Baseball debut with the Giants and hit a home run in his first at-bat, becoming the first Giants player to do so since Will Clark in 1986. Pill was eventually replaced for a relief pitcher, but he ended the night 1-for-3 with two runs batted in on that homer and no strikeouts or walks.
This bat was broken during Brett Pill's third at bat when he lined out. He homered and flew out in his two prior at bats and photos and video show him swinging this same type of bat. There is an excellent chance this is the bat used to hit the debut HR as we can see some matches in the linked video about 15 - 25 seconds in. The black spot on the top of the barrel and the darker grain around the back of the logo appear to match.