Brantly recalls his first MLB at-bat, which came on Aug. 14 against the Phillies at Marlins Park.
In the second inning, Brantly struck out swinging against Kyle Kendrick.
"I was really over-antsy when I first got here," the 23-year-old said. "I've always been kind of a high-energy guy. When I get over-amped, that's when I get into trouble.
"I was facing Kendrick my first day. I will never forget my first at-bat. I came back in and said, 'Man, how am I swinging through those changeups?' Everybody looked at me, and said, 'Changeups? They're coming in at 91, 92 [miles per hour].' My mind was going so quick. I was swinging at the ball right out of [his] hand."
Brantly is now settling into being in the big leagues. The left-handed-hitting rookie extended his hitting streak to seven games with a double in the second inning on Saturday night against the Reds.
The Marlins acquired Brantly from the Tigers on July 23 as part of the Anibal Sanchez/Omar Infante trade.
The Marlins are giving Brantly a look now to see if he will be ready to play on a regular basis in 2013.
Brantly has hit at every level, and once he gained some confidence, it was a matter of time before he had results in the big leagues.
"It's a long season," Brantly said. "During the season, you go through peaks and valleys. You try and ride your peaks out as long as you can, and minimize the valleys."