It happens. Enemies appear out of the mist, initiatives are rolled and then... there's a pause. The referee needs to determine who these dread things put to blade and claw but there is no logic or context for them to decide the target of the awful attack. Often this results in some sort of roll off: each PC is represented by a number, the referee rolls the appropriate die, and whichever PC matches the number rolled gets attacked. Easy, peasy, and done. But what if...
What if this random roll could be mitigated somehow?
I have said, on more than one occasion, that, as a player, the dice are not your friends. To invite a roll of the dice is to invite disaster. This is one occasion during which, conventionally, there is nothing that can be done other than prayer and blood sacrifice to the dice gods. Let's change it a bit.
First, let's recall what is happening, in the fiction. Enemies are attacking. Enemies are attacking without any context that might determine the target of their attack. This last bit is important: we should not be lifting the dice to determine a target if there is a natural, logical target. If we are not availing ourselves of the dice to make that determination, the mitigating mechanic we're about to discuss will not be applicable.
With that out of the way, here's the deal:
Whenever an attack against a random member of the Party (here including retainers, hirelings, kidnapped grandees, yadda, yadda, yadda) is made, a fighter-- prior to the determination of the target is made-- can opt to become the target of the attack; if a determination is made and the target is found to be a thief, the thief can demand one redo of the target determination.
Let's break it down.
If there's a fighter in the party, they can essentially volunteer to be the target of the attack, provided fictional positioning allows for it.
If there is a thief in the party and they get randomly picked, they can make a one-time call to the referee to redo the target selection.
Everyone else, barring magic or prayer, is at the mercy of the dice, as ever it was.
What does it do?
Fighters get to flex their superior armor defenses by stepping into the breach and taking one for the team. Thieves get to lean into being slippery. Remember: this only comes into play when enemy attacks lack reasonable context for selecting targets. This doesn't come up terribly often in my experience. Yours may vary, of course. Also, the referee will have to publicize when a random target is being determined. In my experience, this tends to be vocal already but, if the referee currently holds it close to their vest, they'll have to now declare it openly.
The last thing is just to remember the first thing: this does not trump context. If the fighter or thief is surprised or otherwise unable, due to fictional constraints, to tilt the targeting in their favor then they can't, sorry.