UPDATE
6:21 AM PT -- Authorities in Pittsburgh say the fan is currently at a local Pittsburgh hospital in "critical condition."
No further updates regarding his health were given ... though they added they believe the incident was an accidental one.
An MLB fan sustained significant injuries in a fall from a PNC Park outfield wall on Wednesday night ... and the scene was so horrifying, Pirates manager Derek Shelton asked afterward for "everybody to keep him in their prayers.