9 stress is certainly more than you can mark at once, but clearing out all of your stress between scores can be a bit of a gamble in overindulgence if it's on the low side.
So let's say that one of my PCs, Candlestick, starts a score with like 2 or 3 stress, pushes themselves once, and then has exceptionally bad luck leading a group action or on a resistance roll. That could just be it, right there, marking Trauma on the first roll of the score.
My first read of the rules I thought that meant they were out of the score, but going over the section again, it doesn't seem like that's necessarily the case:
When you suffer TRAUMA, you're taken out of action. You're "left for dead" or otherwise dropped out of the current conflict, only to come back later, shaken and drained. When you return, you have zero stress and your vice has been satisfied for the next downtime.
-- "Trauma", p.13
The mention of downtime is what got me thinking "score", but all that it mentions for scope here is dropping out of "the current conflict", whatever that is. I checked the index for mentions of "conflict" but it only comes up in resolving disagreements between players, which I'm pretty sure doesn't apply here.
So: how long is a character supposed to be out of action when they mark Trauma? The entire score? Less? But if so, how much less?