boating In the collected version of this verse, Kipling headed it— more appropriately— 'Rowing'. It is a scene of extreme effort on the river, more like training on the Thames than leisurely boating in Hyde Park. A modern coach would probably be riding a bicycle and shouting instructions through a megaphone.
pleasant meat good food.
These who ... endure lean days and lives enforced pure Oarsmen in hard training.
curses of the Pit rowing coaches often use robust language to urge on their crews.
Flings forth by number not by name The rowers are addressed by numbers, 2, 3, 4, etc., according to their position in the boat.
shuffle-stocking Untidy, with stockings falling down.
triple-crown The triple crown of the Papacy. Kipling's point is that in enforcing abstinence the dictates of religion are as nothing compared with the discipline of training.