I don't know about the VIX.
Does it anticipate future? Or is it lower because market range smaller today?
Is it leading? When I look at it over long daily chart, looks like it is reactionary?
So maybe next week big move down in SPY. VIX then goes up. As reaction.
Maybe?
The vix is basically the view of traders of expected volatility. If its leading or lagging is difficult to answer easily I think. It just gives a glimpse of the puzzle by providing a number derived from spx option prices (23-37 days).
(although I read in the past some theories on volatility becoming a driver in itself because of deleveraging reactions, which can have snowballing effects (march 20))