逃げちゃダメだ。
I mustn't run away.
✦ AI pragmatic read · suggests Casual
The speaker uses the colloquial contraction ちゃ and plain copula だ, indicating an informal, possibly peer‑to‑peer or older‑to‑younger admonition; it conveys a firm but familiar prohibition rather than a polite instruction.
A starting point, not the final word — open the entry to add your own note if you'd explain it differently.