This will resolve for any event that happens in October that is called an "October Surprise" by more than 2 major news outlets (as subjectively determined by me (or the mods if i am unavailable or incapacitated)). "Early October surprise" or "late October Surprise" won't resolve this. If RFK is affected by an October surprise, it won't resolve this but will be very funny. In the event both candidates are affected by their own separate October Surprises, this will resolve "Both." I will also resolve to "both" if the October Surprise is some non-scandal (e.g. an invasion or a terrorist attack) that affects the messaging in the race, regardless of who it helps or hurts in the race.
I will not bet in this market.
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Thought about it a bit more and I won't N/A this or change it's resolution criteria but I will resolve Both if it's some sort of major shift in tone that doesn't affect any specific candidate or affects both. Instead, I made another question about which party the market will see as being positively affected.
An October Surprise may be deemed as such due to its impact on the overall race, not it's impact on one candidate or the other. How does the market handle this? For example, a terrorist attack or major military conflict would be described by the press as an October Surprise but the impact would be complex.
I suppose some external non-scandal that affects the messaging in the race (e.g., surprise invasion, devastating natural disaster, terrorist attack) would have to resolve to "both," as both candidates have to change their messaging even if one candidate is specifically helped or hurt by it. It might be better if I rewrite that option, though I'm not sure what the best wording for it would be, maybe something like "both (or surprise is not a single-party scandal)"?
Hmm. I'm starting to see an issue going back and looking at past october surprises... These look like they'd be hard to resolve. 2020, even - Trump was undoubtedly affected by catching COVID and nearly dying, but there was also the hunter laptop stuff that would make it pretty likely a "both". 2016 would be really easily a "both" since you had the Podesta leaks and the Access Hollywood tape on the same day. 2012 is hard to resolve since the surprise was both Hurricane Sandy but also decisive government action and government failures before and after Sandy, and under this it'd probably have to resolve "both" despite much more obviously affecting the sitting president. 2008 was probably Obama with the scandal with his half-aunt. 2004 and we get into difficult territory again - the Bin Laden tape (and missing explosives, and reduced price of oil) all obviously impacted Bush, but I can't tell if I'd have to resolve it as "Both" for some other reason. 2000 is easily resolved - reporters found out Bush had a DUI in Maine, so it'd be obviously Bush.
It's looking like there's a not-insignificant chance that this question is going to end up difficult to resolve.