The Paladin fell because...

[Goth Guru]

The paladin falls into being a cavaliere for chaotic nonsense.

The paladin tricked Ravagog into hiding in a portable hole so he could escape his prison. The paladin's wizard friend tossed in an orb of oblivion, then teleported the party away.

[Count Reiner Heydrich]

The paladin fell because he tripped over his own feet!

The paladin agreed to play Blood Bowl (as a member of The Bright Crusaders*).

*= The Bright Crusaders are a team that consists of humans who focus on holding charity events and never play dirty (so, unlike literally everyone else in Blood Bowl, these guys don't make fouls).

[Khāṇa Tsogtsos]

The paladin fell for making the Forces of Righteousness look like total losers, AND (since he was a Paladin of Islam) for handling pig-leather.

The paladin (NOT the same faith as the one above!) ended a tormented undead abomination's reign of terror by defeating him in a drinking-contest.

[Mightypion]

The Paladin fell for comitting substance abuse.

The Paladin held a glorious speech before a climatic battle.

[Waterhammer]

The paladin tripped. And you know…

[I'm Hiding In Your Closet]

Mightypion wrote:

The Paladin held a glorious speech before a climatic battle.

...and fell for not taking the opportunity to proselytize the infidels in his army on behalf of his deity.

The Paladin battled a dragon to a draw, reconciled with and befriended it, and the two started a pizzeria together.

[Fish-Malkovich]

The paladin fell, because all the pizzas he made had pineapple on them.

The paladin single handily brought back every species of animal that went extinct.

[Angrboda Fossey]

That's easy; the paladin fell for defying what was clearly the long-established will of the gods.

The paladin saved a millions of innocents from starvation by curing a blight on an island-nation's crops.