High avg correlation (>0.6)
Risk-off regime. Stocks are one big trade. Diversification fails. Tighten stops, reduce gross exposure, watch for vol expansion.
Low avg correlation (<0.3)
Stock-picker's market. Individual catalysts drive moves. Trade size up on conviction names, use pair trades for relative value.
Correlation breaks
When a normally-correlated pair (NVDA/AMD, MSFT/META, etc) diverges by 2σ from historical norm, it's often a tradable mean-reversion setup. Watch the pair-trade table.