A fight on the morning of his scheduled release is going to raise red flags with staff, and the delay is a direct result of that.
Juvenile facilities take incidents seriously, especially ones that happen right before a release date. The timing is what makes this particularly concerning from their perspective. A fight hours before walking out the door suggests either poor impulse control, unresolved conflict with another resident, or on some level a reluctance to leave. Staff have seen all three, and they are not going to release a kid into the community when his last act inside was a physical altercation.
The honest read on this is that something was going on with him this morning, whether that was anxiety about going home, a situation with another resident that had been building, or something else entirely. Three weeks in a juvenile facility can create its own social dynamics and tensions.
The best move right now is to call the facility and ask to speak with his counselor. Get a clear picture of what happened, what the review process looks like, and what the new timeline is. Staff will typically reach out when they feel he is ready for re-entry, but there is nothing wrong with initiating that conversation yourself. Staying engaged and cooperative with the facility works in your son's favor.
When he does get out, it is worth having a real conversation about what happened this morning and why.