A soldier may take a vow to protect a weaker adventurer if he is up to the task and if he considers the weakling worth protecting, for the common good of the party. The life of the protected may well be saved by the soldier; but nothing is as certain as uncertainty in the chaotic turmoil of a battle.

The protected must be weaker than the protector, and unless she is behind the protector in party the saving will not be possible.