Easily done with the daggers and Alucard at the beginning of the game.
Stand in one place and throw them at zombies, 1 dagger for each zombie and the achievement will pop up.
Daggers can be found on one of the candles on the wall, just break the candle and they should appear.
NOTE: After further realization, the "Cube of Zoe" relic is required for Daggers to spawn out of the candles. The Relic can be found in the first large area, past the cutscene with death. It looks like a cube that's floating and shimmering.