Some spells require the caster to concentrate for the spell effect. If a spell caster is badly hurt he/she may loose concentration. Here are some ideas how to deal with it.
If the caster receives just concussion hits, he/she is able to maintain the concentration. If a critical hit is received, he/she will loose concentration unless the caster is able to perform a successful concentration maneuver.
The skill Meditation-Ki is used for this maneuver. The caster may deceide not to roll for this maneuver. In such case concentraton is lost. To maintain concentration the caster needs to successfully perform the following maneuver:
Critical hit difficulty
A … medium
B … hard
C … very hard
D … extremly hard
E … sheer folly
This means that especially low level spell casters have a very low chance to maintain their concentration after a critical hit.