Momentum crash detector

Scores a sell-off that is speeding up, but reads 0 on every bar with the default inputs.

The indicator reads three lines: the close, a fast rate of change and a slow rate of change. It returns a score only when the fast rate is negative and sits below the slow rate, which means the recent fall is steeper than the longer one. The score is that gap scaled by 100. In every other case it returns 0, and the close only has to exist; its value never enters the score.

How to read it

The line sits in its own pane below the price, not on the candles.
A value above 0 means the market is falling and the short-term rate has dropped below the longer-term rate.
On the explainer preview, where both rate inputs read the raw close, the line is flat at 0 for the whole SPY sample, so it marks no bars.

What it outputs

Crash score: 0 unless the fast rate is negative and below the slow rate; then the gap between the slow and fast rates, times 100.

Pitfalls

In the explainer preview, roc_fast and roc_slow both read the raw close. A price is never below 0 and the inputs match, so the score is always 0. Connect real rate series first.
The name says crash, but the code never checks price level, volatility or volume. It only compares two rate-of-change inputs, so its meaning is only as good as those rates.
The 100 scale assumes fractional rates, as the ROC indicator returns. Rates in other units change the size of the score without changing what it measures.