Crab, or Catch a crab
A rowing error where the rower is unable to timely remove or release the oar blade from the water and the oar blade acts as a brake on the boat until it is removed from the water. This results in slowing the boat down. A severe crab can even eject a rower out of the shell or make the boat capsize (unlikely except in small boats). Occasionally, in a severe crab, the oar handle will knock the rower flat and end up behind him/her, in which case it is referred to as an 'over-the-head crab.'