TOKYO, March 22 (Reuters) - The Bank of Japan bought 50.1 billion yen ($461 million) of Japanese stocks exchange traded funds (ETFs) on Monday, data from the central bank showed. Market players were paying close attention to the BOJ’s stance after it said on Friday it will buy ETFs as needed, ditching a commitment to buy at a rough pace of 6 trillion yen a year. ($1 = 108.69 yen) (Reporting by Hideyuki Sano; Editing by Toby Chopra)