Rowing race between the colleges of Cambridge University.
Twice a year (Lent and Easter) fifteen or so divisions of twenty rowing eights charge down the river cam each trying to bump into the boat in front and not be bumped by the one behind. If they do get hit, they swap places for the next days race. The objective is to be the head of the river.
Each division races once a day for four days. If an eight bumps each day then they get their blades.
The whole affair finishes with a boat club dinner for each college.