In that first assault, Jonathan and his armor-bearer struck down about twenty men over half an acre of land.

Judges 9:54
He quickly called his armor-bearer, saying, "Draw your sword and kill me, lest they say of me, 'A woman killed him.'" So Abimelech's armor-bearer ran his sword through him, and he died.

1 Samuel 14:13
So Jonathan climbed up on his hands and feet, with his armor-bearer behind him. And the Philistines fell before Jonathan, and his armor-bearer followed and finished them off.

1 Samuel 14:15
Then terror struck the Philistines in the camp, in the field, and among all the people. Even those in the outposts and raiding parties trembled. Indeed, the earth quaked and panic spread from God.

And that first slaughter, which Jonathan and his armor bearer made, was about twenty men, within as it were an half acre of land, which a yoke of oxen might plow.