The S&P 500 index (SPX) has been in a lull in August, just hanging out at historic highs around 2190. However, there was a major sell-off, the strongest since late June.SPX Daily Chart 9/12(click to enlarge)Sharp reversals:- Since price found support around 1820 in January, sharp sell-offs have been countered by sharp bullish reversals. - In hindsight we can say that these V-shape reversals suggested a bullish market ahead either as a reversal from the prevailing downtrend or a continuation of the prevailing uptrend. - The most recent V-shape reversal occurred when price fell sharply from above 2100 to 2000. 2000 was a psychological level as well as a support/resistance pivot area. - Back in February, price came down sharply but bounced up just as sharply after it tagged the previous low. Price eventually formed a double bottom.Look for support around 2100:- I would start looking for support around 2100 as price tests a rising trendline.- A bullish divergence between the RSI and price action would increase the likelihood that we see a bounce off the 2100 area. - This is where I would consider a "reactive support". However, just because there could be buying at 2100, doesn't mean that there will be a sharp bullish reversal back into the uptrend like we saw in June. - The only thing I would say is that I think price can hold above 2100 this week.