What is the difference between a fence and a hurdle?

What is the difference between a fence and a hurdle?  In National Hunt racing, participants are required to jump two basic types of obstacle, namely fences and hurdles. Fences, which are jumped in steeplechases, or chases for short, come in three different varieties, plain, open ditch and water jump; with the exception of the water jump, which is optional in any case, they are higher, less rigid and less forgiving than hurdles. A plain fence, which must be at least 4’6″ in height, consists of a rigid frame, made from steel or timber, stuffed with real or artificial birch – the density of which determines the ‘stiffness’ of the fence – and sometimes, but not always, ‘dressed’ with loose spruce topping. An open ditch is simply a plain fence preceded by a shallow ditch, several feet wide, to create a broader, more challenging obstacle.

Hurdles, on the other hand, are lightweight, portable panels of cut brushwood, which are hammered into the ground, side by side, to create a so-called ‘flight’ or hurdles. Each flight of hurdles must stand at least 3’1″ high and at least 30′ wide, but is nonetheless a relatively flimsy obstacle when compared to even the most innocuous steeplechase fence. In a hurdle race, it is not unusual for horses to kick out the top bar or knock individual hurdles flat.