The S&P500 index (SPX) has been trading sideways practically since July 29 and as it failed to break the May 30 High and current Resistance (in fact got rejected near it on August 08), it broke below the 4H MA50 (blue trend-line). Even though the index had broken above its long-term Channel Down on 1D, on the shorter-term such as the 4H time-frame, there are some additional angles to consider before achieving higher targets.
As this chart shows, the 4H RSI has formed a Channel Down while the price traded sideways, struggling to break above the May Resistance. The very same structure was also seen from May 30 to June 08. The bearish RSI made the sideways index trend break below the 4H MA50 and after a dead-cat-bounce, it sold-off aggressively. This time though, the 4H MA200 (orange trend-line) isn't coming from above the 4H MA50 but is instead below it, ready to provide the crucial Support. In the same notion, the 1D MA50 (red trend-line), which already gave a price bounce on July 26.
On any given moment, a break above the May Resistance would be a bullish break-out signal targeting the 1D MA200 (yellow trend-line) for the first time since April 21.