On the 28th of February 2022, the US Government banned United States persons from engaging in transactions with the Central Bank of the Russian Federation. The motive was quoted as "to prohibit American dollar transactions with the Russian central bank".
How exactly does banning American individuals from the Russian central bank translate into prohibiting the Russian Central bank from defending the RUB in the foreign exchange market? Given that the forex market is huge and decentralized, why couldn't the Russian central bank simply sell USD and buy RUB to non-American individuals?