Summer Eights is an inter-collegiate rowing competition held in both Oxford and Cambridge Universities (but independently of each other). While it may most quickly (e.g. when explaining it to a japanese tourist whilst late for a lecture) be described as operating on a league system the mechanics are unique, allowing for a college's rowing performance to be determined over the four-day long event.
A day's racing involves lots of short races which take place in Oxford on the river Isis, starting above the lock at 'Haystack's Corner' and ending below 'Folly Bridge'. This course is slightly under two kilometres long upstream and takes the racing crews past all the college boathouses. Each of these small races involves a division of twelve boats which line up above Haystacks corner with their bows pointing towards the finish line. Each boat is separated from the one behind it by one and a half boat length. In this way a division will span a long section of the river with the lowest boat in the division furthest from the finish line. The coxes of each boat keep themselves from drifting away from their starting position by holding onto pieces of rope tethered to the bank, known as 'bung lines'
The start of each race is signalled by the firing of three guns - at five minutes to go, one minute and race start. When the third gun fires each crew rows as fast as they can towards the finish line with two aims: catch the boat in front of you and prevent the boat behind from catching you. Fortunately (since when the adrenaline's pumping a rower's capacity for doing more than one thing at once drops to zero) these two goals involve much the same thing: rowing as hard as you can.
When a boat catches another they are said to have 'bumped' the boat in front or to have 'been bumped'. A boat 'bumps' another in two ways: either rowing clean past it or by touching any part of the boat in front with any part of the chasing boat. And yes, 'any part' means the blade, rigger, shell or the rowers themselves. A cox catching a blade in the back is a very common and painful occurrence, but is warmly encouraged by coaches for the simple reason that a little bloodlust never did a crew's performance any harm.
When a bump occurs both boats are out of the race and must get out of the racing line as quickly as possible to allow boats behind them to continue. A bumped boat exchanges its position in the division with the boat that bumped it - in this way a good crew will move up the division while worse crews gradually filter down. An 'overbump' is also possible whereby out of four boats the middle two 'bump out' leaving the fourth to try and catch the first. Such an occurrence is relatively rare and is a fantastic experience for the overbumping crew.
A division takes about half an hour to complete, during which time almost anything involving boats may happen. The most amusing scenes are found in the lower divisions where novice crews led by inexperienced and nervous coxes cause general carnage, especially around a section of the river known as the 'Gut'. Here the river narrows and turns simultaneously allowing spectacular overtaking maneuvers for experienced crews but causing horrendous crashes for most. Of course, if two crews become entangled they present a large and slow moving target for subsequent boats propelled by overexcited rowers to crash into and before you know it the race marshalls have something very similar to a log-jam on their hands. Except most log-jams don't have morose, incensed or even tearful (if the onlookers are really lucky) coxes to laugh at.
As the day goes on the rowing quality improves (since lower divisions race first) and the highest places 'on the river' are fought over fiercely. Holding the top spot; that is, first in the first division, is known as being 'Head of the River' and attracts general esteem. However, less able boats still have a goal to aim for, even if they're bottom of the sixth division, in the form of 'getting their blades'. If a crew bumps every day they will have improved their position on the river by at least four places (more in the case of overbumps) and are allowed the privilege of forking out £50 for a set of ornamental oars.
Taking part in a bumps race for the first time is thoroughly terrifying, and subsequent outings become only slightly less so for the veteran rower. The combined possibilities for actual bodily harm, the settling of scores, miraculous victory and hideous defeat are unique to this event. If you can, get to Oxford for the last day. And if you don't like the racing there's always the Pimm's...