At 15 years and 212 days, the young seamer's appearance at Scarborough made him county cricket's youngest post-war player and he turned in an impressive display in the Group C clash. His first involvement came with the bat, edging a pair of boundaries before being run out for 10 in a Yorkshire total of 258 for nine.
Fisher, one of four teenagers in the Tykes XI, then bowled seven overs for 40 runs, trapping Shiv Thakor lbw for his first senior wicket. Leicestershire still managed a three-wicket win with five balls to spare, Greg Smith (58) and Rob Taylor (48no) leading the way.
Yorkshire have lost five of their six outings in the competition and are above only the semi-professional Unicorns who lost by 85 runs to Glamorgan. The Welsh side posted 300 for six, Chris Cooke falling two short of his century and Dominic Reed taking five for 31 while his colleagues struggled.
Scott Elstone (48) and Garry Park (74) briefly shone together but the Unicorns finished well short on 215 for nine after Graham Wagg claimed four wickets.
Group B front-runners Derbyshire defeated Essex by 63 runs at Leek. Shivnarine Chanderpaul's unbeaten 85 and Wes Durston's big-hitting 71 helped Derbyshire to an imposing 321 for six - an innings that included 11 sixes and 28 fours.
Mark Pettini managed 88 in response but Essex were dismissed for 258 in pursuit of victory, Mark Footitt and Alex Hughes sharing six wickets.
Lancashire recorded their second 40-over win of the season with a five-wicket defeat of Surrey at Guildford.
The Red Rose kept their opponents to 264 for eight and reeled in the target with 15 balls to spare.
The day had started brightly for Surrey, with Steven Davies and Jason Roy putting on a century opening stand, but regular wickets - including Ricky Ponting run out for 17 - halted their progress. Lancashire's own imported talent fared better, with Ashwell Prince's 71 and Simon Katich's 57 not out seeing them over the line.
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