When you fight someone and win loot, are you taking it from the person you fought?

When you get an item from winning a fight, you aren't taking the item from the other person's inventory, no. Anything you find is just created out of thin air and added to your inventory. You can loot just about anything in a fight. I've even looted drop loot that I had not yet received from doing jobs!

UPDATE: With the addition of Cuba, I've noticed that when fighting in Cuba, you seem to loot Cuban stuff. You get NY stuff when fighting in NY!

So don't worry about your inventory going down when people attack you -- the only things that can be lost when fighting are health & cash!

Here's a screenshot of me looting an Armored Truck from a fight I won -- note the message just says someone in your mafia 'found' it and it was added to my inventory. The person I fought didn't lose an Amored Truck. Finders keepers! :)