From:
http://forum.melee.org/beginner's-help-and-guides/game-mechanic-megathread!/- Knockdown has a chance to knock down enemy on swings. This depends on weapon mass, but does contain a significant random element.
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The mechanic for knockdown is (rand(0.0, 1.0) < min(item_weight * 0.33, 2.0) * min((raw_damage - 20.0) * 0.5, 10.0) * 0.015) according to Paul (
http://forum.c-rpg.net/index.php/topic,20938.msg299772.html#msg299772). How this kind of equation works is that the higher the right side value is, the higher the chance of success is. Percentual chance of success is the right side of equation.
This means two things affect knockdown chance. Weight of the item and raw damage of the swing. If we assume a hit does at least 40 raw damage, which is very likely for a decent hit from almost any weapon with knockdown with 5 PS or so, the knockdown chance boils down to min(item_weight * 0.33, 2.0) * 0.15. This means that the maximum weight for this calculation is 6. This results in the knockdown chance being 0.0495 * item_weight, meaing 4.95% chance of knockdown per item weight (this could be rounded to 5% like Paul did, but 0.33 isnt 1/3 for exact chance). This allows tabling some weights:
Weight 1.5 (Hammer, Club): 7.425%
Weight 2.5 (Flanged Mace, Iron Mace, Goedendag): 12.375%
Weight 3 (Warhammer, Long Hafterd Spiked Mace): 14.85%
Weight 4.5 (Long Iron Mace, Bar Mace: 22.275%
Weight 6 and above (every crushthrough weapon): 29.7%
The effect of damage is a multiplier to this chance, min((raw_damage - 20.0) * 0.5, 10.0). At 40 or more raw damage the multiplier is it's maximum (10), resulting in our assumed values above. Attacks below 20 raw damage cause the multiplier to be 0, meaning 0% chance of knockdown. Between 20 and 40 raw damage each point of raw damage increases the multiplier by 0.05. This means that the knockdown chance calculated above goes down by 5% per point of raw damage below 40 (for example 38 damage attack with a warhammer means 14.85% * 0.9 = 13.365% chance of knockdown). As said above though, in most practical cases most of these weapons will deal at least 40 raw damage with a decent hit, so that part of the equation is fairly meaningless.
