catch a crab
v. phr.— «And they oohed with disappointment when another boat stopped dead in the water as one of the rowers “caught a crab” as they say in the sport: An oar caught water and was pulled downward resulting in an urgent need to halt the boat.» —“They pull for East Hartford High” by John Karas East Hartford Gazette (Connecticut) Oct. 30, 2008. (source: Double-Tongued Dictionary)
This phrase appears in “Through the Looking Glass”, Chapter 5 (in which Alice suddenly finds herself rowing in a boat with the Sheep):
“‘Feather! Feather!’ the Sheep cried again, taking more needles. ‘You’ll be catching a crab directly.'”
alot of older inmates use it on the newer inmates “catch a crab”,
seeking out fresh meat or punk them out.