Truck Brawler Trophy in Uncharted 3: Drake's Deception

This trophy is earned in Chapter 20 - Caravan.

As Chapter 20 begins, you will be on horseback with Salim, chasing down the convoy through the canyons of Yemen. You will eventually catch the trucks by holding up on to make your horse gallop faster and continue to ride until you are right up against the back of the truck. When you are in position, press to jump from the horse to the truck and hit to pull the bad guy over the edge for an instant kill or hop over if they are further back and melee attack them to death. When you are done, jump back over the side of the truck to your horse and do same with the next one.

You can go ahead and kill the annoying dudes on the motorcycles with gunfire as they don't count for this anyway and it's not a chain kill requirement so you can get gun kills in between. There is a part where you can not go further until you down two trucks with an RPG, you will not have killed 10 up to this point and it seems like they are the last trucks but rest assured that you will catch up to more further down the road. Just keep jumping over to the trucks and melee killing the passengers on the back of each instead of shooting from your steed, you should get this trophy with a couple of trucks left to spare.

When you kill the final truck based enemy with a melee attack/stealth grab, the trophy will unlock.

However, if you aren't worried about dying and are not going for the Survivor trophy then there is a much more pragmatic way of earning the trophy by simply killing yourself after you stealth kill the very first guy in the first truck you come to. Here's a video showing this method, courtesy of PowerPyx: