1 Samuel 14:14

And that first strike , which Jonathan and his armor-bearer made , killed about twenty men within as it were half a furrow’s length in an acre of land .

In that first attack Jonathan and his armor-bearer killed some twenty men in an area of about half an acre.

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