Guarding
Guarding (aka blocking) is a core mechanic of Jcraft PvP that serves as the users most valuable source of defense in a Stand users arsenal.
Usage
A stand that's Guarding will give the player Resistance IV which is effectively 80% damage negation. A player that's blocking will also be provided with a heavy amount of Slowness as well, heavily reducing your mobility.
Guarding, because it gives resistance, reduces all incoming damage by 80%. This includes; Lava, Fall damage, and burning. However, void damage and starvation damage will ignore the resistance. As well as The World: Over Heaven's singularity attack.
A Stand that's Guarding will reflect any vanilla projectile that is shot at it. This is done in two different ways such as having an arrow deflected in the direction the player is looking, or a blaze fireball sliding down your stand until it reaches the floor.
Irregularities
Some Stands lack the ability to block all together:
The Fool blocks all guardable damage during its block as it receives Resistance V. However, it's also slowed down to the point where the user is immobile while it's active.
Purple Haze, while capable of blocking, is uncontrollable and favors doing moves over blocking in a majority of situations.
The Hand, because it has moves that deal void damage, can ignore the damage resistance that block gives during some of its moves.
Cream can still block while the user is inside of cream, although it's less visually obvious to the user.