The latest example came on October 16, when the By October 17, the VIX was back down to its level from days earlier, before US President Donald Trump started to upset markets with threats to impose higher tariffs on China. UBS strategists including Kieran Diamond highlighted that S&P 500 option market makers on Oct. 16 became shorter volatility as the market fell, which could have exacerbated the VIX jump as those positions were covered. Furthermore, dealers were probably short VIX calls and the hedging o ...