For non-DCI play, Soresu Style Mastery is per the glossary definition listed below:
Soresu Style MasteryReplace the rulebook entry with the following: Soresu Style Mastery: When this character is hit by an attack, it takes no damage with a save of 11.
This is found here:
Holocron: ErrataFor DCI tournaments, now sponsored by SWMGamers, you must follow the DCI Floor Rules. Here is the section on SSM:
616. Game Rule Modifications for All Tournaments
Soresu Style Mastery
Soresu Style Mastery only affects nonmelee attacks in DCI-sanctioned tournament play.
This is found here:
Holocron: DCI Floor Rules