S&P is making a five-wave drop from the 4819 high; we see current sharp drop as wave (3), with possible support around the 4350/4360 lvl., from where a new wave (4) correction can start unfolding, and look for resistance at the middle parellel channel line.
Alternate scenario: Wave (3) is very sharp, which means price could extend wave (3) and deeper levels can be seen, before a correction of a wave (4) of red wave A may show up. In this case possible support for wave (3) is around the 4350/4278 region, level of a former higher degree wave 4.