My field has a fairly clear surrender rule. If you are within 15-20 feet and you don't think you can close the gap to barrel tag/knife/slap for the out you can offer the surrender. If the person being surrendered turns or does anything other than surrender, you can shoot them, but you have to be merciful about it ie. shoot the pack or 2 shots tops. There is also the stipulation that trying to surrender someone from their front or while they're in cover doesn't work and shouldn't be tried.