Imperial Crusader

[Produces the following effects when worn with Imperial gaiters, Imperial helmet, Imperial gauntlets and Imperial boots: Dex -2, Str +2, P.Def +8%, Max HP +445. Sleep/Hold Resistance -70%. Poison/Bleeding -80% when Imperial Shield is also equipped.]

What's that resistance -70% and -80% about? Why does a S grade armor have that kind of effect?

Hmm you misunderstood and so have many others. It's how it gets translated by a korean who speaks english and not a englishman who speaks korean :D.

It is +70% and +80% if you look at the wording carefully...

It says:

Sleep/Hold Probability -70%

That's probability, the reverse of resistance :p