There is a "Hidden Support" level that I have published many times here at TradingView and it comes from the large, long term buyers who show up to absorb supply from weak, short-term sellers. The "hidden tracks" that these buyers leave in the market, in this case the SPY (S&P500) revealing their presence is the action of the VIX indicator which retraces 75% of the last 5 point rally.
If you go back and see my other publications on this phenomena, then you can become more familiar with the power of this simple, yet powerful observation.