YAOSC (Yet Another Old School Clone)
Normally, taking damage in a given combat round means the character cannot cast spells by any means other than device for the rest of that round. Those who invest in this skill may check Concentration each time they take damage; a success allows them to ignore that wound and attempt casting by other means. Concentration is rolled separately for each wound, and any failure prevents casting. Wounds received between beginning casting and the spell’s coming into effect apply a -2 penalty to the roll.
In addition, if circumstances and the player’s role-playing make it appropriate, the YAM may allow a character to check Concentration, with success granting a +1 bonus to another roll (common examples include skill checks, Psychic or Corruption saves, or perhaps a ranged attack in a target competition). Application is left to the YAM’s discretion, but never more than once per scene.