So you’ve ended up one lone gunner verses multiple enemies. What do you do now? First off, don’t panic, you can win this. Just because you are outgunned 5 to 1, you can still win.
After not panicking, the next thing you need to do is get a bearing on your surroundings. Are you still hidden? Do the other guys know where you are? How many of them do you know are still alive? Once you have taken stock of these factors, figure out if there is a spot you can pull back you can take them out one at a time. No? They know where you are and are advancing on your location as you think this through? Can you defend the spot you are and take out 1 or 2 of them? If so stay and try to get a few, if not get ready to run. Either spray and run, or just run. Running is a great option. If they try to chase they will be giving their location away. If they try to shoot they will likely miss you and you will be able to find a good ambush spot.
Do not be afraid to fire and retreat multiple times, they will try something stupid eventually. Never try to fight a fight you know you can’t win, unless you know there are reinforcements on the way.
If you run out of space to run, you’ll need to try something a little more drastic. Maybe try to trick the enemy. Leave your primary somewhere with your hat at a tree and move to a different location with your sidearm ready. You might be leaving yourself with little chance, but better than none.
Overall your best bet is retreating as much as possible. One vs many is a tough place to be, especially if your location is known.