Stealth
Only the first attack made under Stealth qualifies from the following rules. Other attacks are treated normally.
Out of Combat
Outside of combat situations, attacks made under Stealth Jutsu are unclashable unless the target has 20 Sensory active.
In Combat
While in combat, it's easier to react to attacks that you don't know about. However, without 20 Sensory, you cannot convert Actions to Reactions, meaning to clash Stealth attacks only your base reactions are usable. In addition, if you aren't aware of an attack, you can only clash its DR to a minimum of 1.
However, armour (Including ECM + Impervious armour) and defensive Jutsu are able to reduce the DR of a Stealth attack to 0, provided they were active on a turn prior to when they are being attacked.
Seeing through Stealth
To see through a Stealth Jutsu, your Sensory must be greater than the Chakra Control of the person you're trying to see through. If someone is using a Capstone Stealth technique, you need a Capstone Sensory technique to see through it.