Question: In Crawl, players are given blood to spend at the blacksmith. How exactly do you gain blood? If it's from combat, how much do you get and how is it determined? Per kill? Per hit? Can both the monsters and the human players get it?

Answer: 
Blood is awarded for every encounter (room where enemies spawn) to each evil spirit player based on how much damage they did to the current hero. I don't have any definitive data, but from what I've observed I'm pretty confident that it is not based on your level. However, as you get more vitae, you will obviously deal more damage to the hero with better monsters, so it indirectly scales with your level. You can also get blood just for dealing minor damage to a hero with traps while he runs through a room.

In case you did not know, vitae is awarded based on how much experience the hero(s) gained during the dungeon level. So, it makes it very hard for a hero to win if the hero's body keeps changing hands often, because everyone else's monsters get much more powerful while hero experience gained is spread amongst all the players. If you plan on winning as the hero, take my advice: **don't die.** If you see the hero changing hands a lot, it might be best to bank on good ol' Kourok.
I believe it's per hit on the human, and it either scales with player level, dungeon level, or damage dealt. I have gotten blood as the human, both in blood fountain rooms, and the rooms that have a statue but no glyphs. I'm still trying to figure it out for sure, but I hope this helps!