On the day he was introduced as the new Mets manager back in November, Terry Collins emphasized the importance of fundamentals. So a day after reportedly ripping into his team in the clubhouse, he must be in hell right now: The Mets dropped a doubleheader to the Rockies yesterday — that’s five straight losses and eight out of their last nine — and did so in particularly sloppy fashion. (Meanwhile, fans at Citi Field chanted, “Sell the team,” though such chants are pretty much inevitable this season.) Collins indicated afterward that extra fielding practice is warranted, and it’s hard to disagree. Though, unfortunately, that won’t address all of his other concerns, as expressed on Wednesday night.