So let's take your standard human fighter. Standard array, STR 16 (15 + human bonus), CON 14 (13 + human bonus). We'll give him a sword, chain mail, and shield. His attack bonus is +5, average damage is 7, AC is 18, and HP is 12. We'll send him against a mob of Commoners (To-hit +2, dmg 2, AC 10, HP 4). We'll use the mob attack rules.4 commoners are needed to hit our fighter once. Our fighter will hit a commoner 75%, so we'll say he hits 3 every 4 turns. And let's give the mob an advantage and say he misses the first one. Now, every time he hits, he automatically kills a commoner since his minimum damage is 4. So we'll say that a new commoners join the fray every time one is killed, to keep their numbers at at least 4.After 6 turns, the vanilla 1st-level fighter has died. It's taken 7 commoners total, and he's killed 4 of them. Frankly that's pretty bad ass. Heck, give him the defense fighting style and now it takes 8 commoners to take him down. And note that if you stop at 7, he kills them all and escapes alive.Let's kick it up to 5th level and give the fighter his extra attack and action surge. By this time, he can afford plate. His STR is now 18. Now he's to-hit +7, AC 21, HP 44. It takes 10 commoners to hit him once. We'll give the mob the advantage and round down so he's still hitting once every four turns.After 22 turns, our fighter is dead. He's killed 32 commoners, and it's taken 42 to bring him down. If you stop at 41, he kills them all and escapes alive.10th level! STR is now 20, CON is 16. To-hit +9; he hits 19 commoners every 20 rounds. HP 81. Let's give him a +1 shield, for an AC of 22. Now it takes 20 commoners to hit him once!After 41 rounds, our fighter is dead. He's killed 78 commoners, and it's taken 98 to bring him down. Stop at 97, and he kills them all and escapes alive. At 11th level, with another extra attack, he kills 127 out of 147. Stop at 146, and he kills them all.