Scorched earth

[PyroStock]

Perhaps see it as their last dying wish. When people request to be buried with their expensive jewelry it doesn't do them any good when they're dead and they're not doing it to financially hurt their heirs.

Perhaps it's not so much they want to see you lose, but rather they want to see player x win. When they throw in the towel I don't see the difference between them giving all their gold/gems to their conqueror or their conqueror's enemy or someone else.

Those are just some ideas, but basically unless the person actually says they're doing it to hurt/spite you I wouldn't assume that's the case. They could have a rational reason or an irrational reason completely unrelated to bad sportsmanship/spite. They've failed... and been defeated, give them the benefit of the doubt.

You could inquisitively ask that person directly in private after the game. That's the best way to get into their head.