what does it mean-> to inject fresh blood by appointing outsiders to the notoriously closed
I read an article about Sumo Wrestles, and found a difficult sentence. here it is, "Many urged the JSA (Japan Sumo Associaton) to inject fresh blood by appointing outsiders to the notoriously closed body."
the context is Japanese society urge the JSA to reform the sport because recently some foreign sumo wrestlers have done some gambling that seems to involving the Yakuza gangster.
"To inject fresh body" and "appointing outsiders to the notoriously closed body". Are they an idiom? Could anybody help me explaining the meaning? thank you in advance.