Miley Cyrus' fiance Liam Hemsworth
rocked another man HARD in the face during a ferocious street fight ... and TMZ
has footage of the violent altercation. 
It all went down early Sunday morning in Philly -- sources on the scene
tell TMZ, Liam had just left a bar when he confronted a guy he thought had
thrown a rock at him and his friend. In the video, the punchee is on the ground
clinging to Liam's leg ... until Liam plows a fist into his face, and pushes
his head down toward the asphalt. Liam's friend helped hold the guy down. Cops
quickly arrived and dispersed the crowd, but made no arrests. Liam took off
with his friend.After the fight, the victim doesn't seem to comprehend he got
his ass kicked, drunkenly slurring, "I don't think [Liam] fared much
better." (Hint: yes, he did.)

We couldn't track down the victim to ask if he plans to file
a police report -- but Philly PD tells us nothing's been filed so far.By the
way, our source on the scene says no one saw a rock get thrown.We've made
multiple calls to Liam's camp