On a break out of a support like that, we usually search an opportunity to enter short. But here is the problem :
- The previous peak (2154.80 points) seems too far to put a stop above it. The first obstacle is located at the 61,8% Fibonnaci retracement of the previous wave that took place after the Brexit referendum. The Reward/Risk ratio is under 1 on the current chart (daily candles). Better not to trade that configuration.
As long as the SPX does not draw an other top, it does not sound to be a good idea to enter short. For those who are already short, the invalidation is the peak at 2154.80 points ; if it is passed the downside trend would be weakened a lot. Your stop order could be placed above that price.
Stay tuned to take into advantage of the proximity of a support (major support is of course preferred) or the formation of a peak. You should have both dynamic and timing to initiate your position.