catch a crab

catch a crab (third-person singular simple present catches a crab, present participle catching a crab, simple past and past participle caught a crab)

1. (rowing) To strike the blade of the oar against the water when moving the oar back between power strokes.
   • 2014, Pip Harry, Head of the River, page 82:

     I blast off the first few strokes with all the anger and frustration I feel towards Rachel. It works against me. I catch a crab and totally lose it. The boat swings sideways and we have to easy oar or risk slamming into the bank.