L ast Saturday night in Manchester, Zak Chelli, a 28-year-old supply teacher from Fulham, produced one of the sporting upsets of the year when he knocked out Cuba’s esteemed David Morrell in a stoppage as shocking as it was compelling. Chelli had been offered the fight two weeks earlier and despite the limited preparation he proved himself a formidable late replacement. Morrell was ahead on the scorecards, but he was hurt badly in the ninth round. In the 10th and last, Mr Chelli – as he is known to his pupils – delivered a blistering lesson before Morrell was rescued by the referee. A joyous Chelli exclaimed he had just done what even David Benavidez could not manage. Last year, Morrell suffered the only previous loss of his career when the imposing Benavidez beat him on points. But Morrell had knocked down Benavidez, one of the most feared fighters around, to burnish his own reputation.…