Was it bitten/eaten by another caterpillar? Or did it pupate wrong? How can we tell?
The first step is to look below the chrysalis. Is there a black stain?
If a chrysalis or pre-pupa (J’ing caterpillar) is partially eaten, it will leak hemolymph (blood). They have an open circulatory system. Their hemolymph is not in veins. It flows openly in the caterpillar’s body. When the cuticle (skin) is ruptured by anything, it leaks hemolymph. At first this liquid is a yellow-green color which turns dark/black within 5 minutes.
If the chrysalis didn’t pupate properly, it often has a gap in the middle, on the belly/leg side. Hemolymph doesn’t leak from the chrysalis simply because the cuticle/skin did not break.