TLDR: it's not always "short gamma", but perhaps there is something to it this time in explaining the outsized move in the $VIX on Friday. Have seen some good discussion on the behavior of the VIX on Friday when it had a move that far outstripped what would have been expected given the relatively modest move lower in the SPX. Typical VIX beta per 1% move in SPX is 5-10. at one point on Friday, the VIX was up almost 30% on down 60bps in the SPX. that's way out of line vs history. The next question is "why?" here we can approach from two ways. first, "new news"...ie, what did the market learn that put it in risk-off? we can advance all of the usual suspects...pod unwinds, crude, Coreweave, etc. But why such a strong move in VIX relative to SPX? I am always careful to advance the stock answer of "positioning" as a cause. In the derivs space, it can't always be "gamma did it"...there are just so many cross-currents that complicate getting a true read. In the limit, it's as clear as day that positioning did do it on the volmagedon day of Feb 5, 2018. Friday is nothing like that, but it could be the case that dealers hedging Oct VIX calls that they were short might have exacerbated the move. I can say with certainty that dealers are short a substantial amount of these. they are short "VIX gamma" --> they are short calls, long VIX futures and forced to aggressively buy VIX futures as the Oct VIX future rises and the delta on the calls they are short quickly rises. I've simulated this below using the Oct 20 call. assuming a "hedger" was short the call and long Oct VIX future, I show how the hedger would have had to buy and sell VIX futures as the option delta moved. you can see the delta gap from 0.2 all the way to almost 0.7 in a hurry, requiring rapid buying of futures to stay delta-neutral. that delta then quickly falls to 0.4, requiring unwinding of those futures. from the 17 to 25 strike, there are 1.8mln Oct calls open. we have to be careful not to double count, as these could be parts of spreads (ie, the Oct 17-22). we also don't really know how they are being risk managed. it's naive to think that the long side doesn't hedge but the short side does. we also have no insight on all the "dark matter" in VIX...that is, the substantial exposures that result via sell-side QIS desks. It's always very difficult to disentangle the "why" of an outsized move. That said, I'm more open-minded than usual that positioning, coupled with timing (this occurred right near Oct expiry, creating an especially large amount of short VIX gamma) may have played a role. We will see what happens Monday!