Weird hit chance calculation

[12]

So there I was trying to hit a guy with a sledgehammer. Starting combat, I see a 95% chance to hit, but as soon as I take a step towards him it changes to 17%. Never noticed this kind of behavior before. I presume it's his dodge kicking in but how does it work exactly? On a side note, is it even legal for him to be this dodgy?

[12]

Unseen attackers can't be dodged

Makes sense, doesn't it? Anyway, I got him with a taser/flashbang+Pummel combo. My 87 effective melee skill and 17% hit chance puts him at ~240 dodge which makes him one dodgy 'tectorate can.