Note the difference in calculated weekly performance. The top chart is a bottom up calculation by finviz.com generated using all the available stocks within each of their sector categories. The second chart is from stockcharts.com and it is the trailing 5 day return of the S&P SPDR Sector ETF's relative to ( SPY ).
After that clarification, we can clearly see the selling is concentrated in the Energy ( XLE ) and Basic Materials ( XLB ) sectors. This reflects current analyst and investor sentiment regarding potential 'demand slow down' in the face of rising raw material supply.
Also note the strong relative performance within utilities ( XLU ), cyclicals aka consumer discretionary ( XLY ) and consumer staples ( XLP ). This indicates buying based on two trends.
1) The US consumer is back in a major way due to the continued persistent decline in oil prices (more on that later).
2) Defensive re-balancing taking place (read: lower expected risk). The correlation between broad market weakness and defensive sectors like consumer staples/utilities is buoyed by the following simple concept:
A LOT of the largest institutional investors (mutual funds, pension funds, insurance funds) have "long only", "fully invested", or "cash balance maximums" mandates imposed on their stock investment strategies. Therefore profit taking, or risk reduction, means they cannot sit on excess cash. It must be reinvested. Well that means if, as a portfolio manager, you believe market risk (volatility) is high (increasing), considering the aforementioned constraints, you must decrease your exposure to stocks that are really sensitive to market changes (high-beta, growth, momentum, high leverage) and increase your exposure to stocks that are less sensitive to market changes (low-beta, value, defensive, low leverage).
See below: