It's been awhile since there was a genuinely bad day for US equities but today is heading in that direction. There is talk of heavy selling on rebalancing flows into quarter end. That same thing could be putting a bid into bonds today.
You also have investors worried about a market that's moved too far too fast. At the open today, the S&P 500 was just 8% away from a new all-time high.
J.P. Morgan expects asset managers and pension funds to sell $150 billion of equities into quarter end in rebalancing towards bonds. That's not an enormous figure but it's enough to get people thinking about taking profits in a one-way market.
So far this month, the trade has been to buy the dip but those buyers aren't showing up today. Even with the selling though, we're still not back to Thursday's opening level.