But then the University of Florida linebacker realised the woman - who was being pressed against the dumpster - was unconscious, according to CBS Miami.
"I mean, at that point, I'm like, this isn't right," Garcia told CBS affiliate WFOR-TV. "This girl is probably drunk, there's no possible way she could've given consent."
"I grabbed the guy by the shoulder and said, 'Get off of her, this isn't right,' and the guy yelled at me like, 'Mind your own business,' " Garcia said. "He pulled away from the girl, and then he got aggressive with me. He tried to throw a few punches; his friends were holding him back."
Garcia told the Gainesville Sun that the man was intoxicated and that after swinging at Garcia, he slipped and "busted his face on the wall".
The victim, according to a police reported cited by the Sun, had difficulty speaking, was unable to walk and struggled to keep her eyes open.
The report states that the alleged assault, which took place behind a bar called 101 Cantina, was captured on video.
"Upon viewing the videos, it is clear the victim was mentally and physically unable to give consent due to her level of intoxication," the police report states, according to the Sun. "The victim was slumping over and unable to hold up her head. The (defendant) can be seen pushing the victim back up. . . . When pushed back up the victim's eyes were closed, and her head fell back against the dumpster."
The Sun reported that investigators said they "have reason to believe" Shaw may have sexually assaulted other women.
Shaw told police the woman initiated the contact by pulling him behind the dumpster while he was walking through the alley, the paper reported. Beyond kissing, he denied having sexual contact with the woman - an assertion that is "completely contradicted" by video evidence, according to police.
Citing a police report, the Sun said the victim told police she did not consent to sex and even tried to rebuff Shaw "but was physically helpless because she was going in and out of consciousness due to her level of intoxication".
Garcia told WTLV that Shaw's friends were present at the time of the attack.
"They were there on the other side of the dumpster," he told WFOR-TV. "Maybe they didn't see it, I can't say 100 percent, but they were there."
Garcia's cousin, Zach Schabbel, told the station he wasn't surprised his relative had done the right thing in a moment of crisis.
"He's a stand-up guy," he said. "You know, always been that way since we were babies. Like, if we'd ever get into some type of trouble, he'd always be the first one to step out and speak. He's always been vocal. I'm not honestly surprised."
Garcia is a walk-on player on the University of Florida football team, according to ESPN. He appeared in the team's 41-7 loss to Michigan in last year's Buffalo Wild Wings Citrus Bowl, ESPN reported.
The athlete told WFOR-TV he had some advice for young people who are out drinking.
"It's important that you don't leave without any friends," he said. "I mean, this girl, her friends had completely left her at the bar alone when she was blackout drunk."