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10. Rowing. to catch (rarely cut) a crab: to make a faulty stroke in rowing whereby the oar becomes jammed under water. The resistance of the water against the blade drives the handle against the rower's body with sufficient force (if the boat be in rapid motion) to throw him back out of his seat, and to endanger the capsizing of the boat.The phrase is not uncommonly applied, from similarity of result, to the action of missing the water with the stroke, or to any other action which causes the rower to fall backward; but this (though found in Dictionaries from Grose onward) is an improper use by the uninitiated.The phrase probably originated in the humorous suggestion that the rower had caught a crab, which was holding his oar down under water; it does not appear to have any historical connection with the Italian pigliare un granchio ‘to catch a crab’, to make a big blunder or complete mistake, ‘toto cælo errare’; all the quots. given by Manuzzi for this phrase are figurative, of conduct, action, etc., e.g. ‘In nessun’ altra cosa l'uom più erra, piglia piu granchi, e fa maggior marroni, che nella cosa della guerra’ (i.e. In no other thing does man err more, catch more crabs, and make greater blunders [literally spades], than in the matter of war).