BABIP is often incorrectly thought to mean batting average on balls in play, but it is in fact a play on the old Saxon saying: "I've had it; I'll bap it."
The term was popularized in the 10th century epic Vandergurd, or The King's Vanguard. It centers around the title character "Vandergurd," from whom we get the word "vanguard." Vandergurd, a sort of super-warrior, battles a monster serpent (often mistranslated "dragon") much in the vein of Beowulf, a similar epic poem circulating Britain and Northern Europe at that time.
Here is an excerpt of Vandergurd from Alfred L. Thompson's 1956 translation:
Spake the king: "He'll [the serpent will] not muster the needed vim. He'll not have the requisition shell to deflect my steel."
And so the sent forth Vandergurd into the blackened valley. The warrior stepped beside the ashen rivers and weaved between the slaggened hillsides. The fires of war had become the snake's trail. Vandergurd happened upon the dead village of Spaekerstroth, home of Lord Errolite, where nay a single bone retained its flesh and nay a single home bore a timber unburned.
Vandergurd slapped the ground with his thundering axe and split the ground deep. He pressed the bones of the villagers into the crevice and closed the earth with boulder.
[He then sings an embedded tale about Illuster the Son of Hope. And as with many oral stories that sport embeded stories, the song has little to do with the present scene and lasts over 143 lines.]
The mountains trembled as Vandergurd drew his axe from the ground, and over the graves of his slain countrymen, he vowed across the heavens:
"Sky burn light,
earth open wide,
show the serpent's den
that I might make right.
Enough is done.
I've seen enough.
I've got my axe,
I'll cut it rough*."
*The more famous, though genuinely worse, Lord Tennyson translation says, "It's sunny; it's clear; I see the dragon's home right there. And I've had it; I'll bap it."