[ by Melanie Gretchen ] Thousands of CME Group's traders walked out of its Eurodollar options pit on Friday to protest a block trade the day before.  On Thursday, prices for the block trades of options on Eurodollar futures were higher than offers in the pit, which wouldn’t be allowed in open-outcry trading, Rocco Chierici, a broker at R.J. O’Brien & Associates on the floor of the Chicago Mercantile Exchange, said in a telephone interview. What's At Stake. Six block trades totaling 215,200 options traded at 8:11 a.m. Chicago time on Thursday, according to CME Group’s website.  The trade was rolling positions from April contracts, which expired today, into June contracts. "These guys that stand in there all day and make prices would have loved to participate in that particular price, but they weren’t able to," Mr. Chierici said.  "There are rules that prohibit that in the pit, but you can circumvent the pit” in a block trade, he said.  "I believe they wanted to make the point that the system is not fair." Above Board. Michael Shore, a CME Group spokesman defended the trade in an e-mail: "The block trade in question was managed by longstanding rules and processes of our exchanges.  It was a legitimate, well-managed trade, which was executed within one tick of the market and in one trade." Other traders continued to help buy and sell options on Eurodollars, which are contracts tied to three-month expectations for interest rates, Mr. Shore said. To date, CME Group has seen demand for Eurodollars, once the largest contract by volume, drop as the Federal Reserve has kept its benchmark interest rate near zero since December 2008.  Eurodollar options volume last month averaged 811,000 contracts per day, compared with 1.3 million on average in the same month in 2007, according to CME statements. For further details, go to [Reuters, 4/13/12].