The scrum half is in essence the lynch pin of a rugby team. It is his or her function to link the awesome power of the pack with the lithe, silky skills of the three-quarters (via a poncy character known as a fly-half, but that's another guide for another day). Unless you are playing in New Zealand and Australia, where he is the only half back, and links the awesome power of the pack with a couple of math graduates that think they are slightly better than him, but not as good as the players outside themselves.
All very confusing. Which sums up scrum-half play in a nutshell. Should he pass? Should he kick? Should he run? And whichever tactic is chosen, he's guaranteed to upset at least two-thirds of his team as they would have done something completely different. (Especially the second rows, who never run anywhere anyway, can't pass for toffee, and wouldn't know how to kick if you asked them.) This is not helped by the schizophrenic nature of the scrum-half's position: is he a ninth forward, or an eighth back? Or perhaps a second ball (as often happens when playing behind a soundly-beaten pack)?
Scrum halves are always Napoleonic in stature. That is, short little bastards always causing strife, occasionally one-handed. They are very stroppy characters, always looking for a fight, and when having found one drags the nearest prop in to sort it out for him. They must have an A-level in niggling, treading on their opponents' feet and kicking loose-head props in the shins when the ref isn't looking.
Every scrum half is a frustrated No. 8. However, nature was cruel and only gave the player five foot two inches of height to use. This never stops scrum halves from playing like No. 8s when given the chance - i.e. running away from support on looping runs, and attempting to tackle the biggest player on the opposite side head on at pace.
The most important part of a scrum half is his mouth. This is so he can spend eighty minutes a week telling other players what they should be doing, especially the incredibly heroic props that arrive late to each ruck and maul because they have single-handedly just gotten up last from the previous one. A non-stop stream of advice can be heard from a scrum-half advising players of which opponent to tackle, where the ball is, where he wants it, which way to go, which arm to bite, etc. Great consternation and abuse will follow if these instructions are not followed instantaneously and fully. However, advice given to a scrum half, such as "pass right, three man overlap" will be studiously ignored, such as box-kicking, as the scrum half has a better vision of the game whilst being surrounded by large forwards than some silly nonce of a centre with nothing near him for twenty yards except an undefended goal line. The kick will be defended with the retort "I could see that their full back was out of position and I wanted to bury him to put him off his game."
Scrum halves are often described as terriers. This is because they are short little yappy things that leave their owners in the shit half the time, and smell.
Scrum halves must have a distinguishing feature. Welsh scrum halves must have large and ridiculous moustaches and sideburns. Scottish scrum halves must have hairy knees (not difficult being Scottish). Irish scrum halves must have foreign sounding names; they can never be called O'Reardon, or O'Reilly, or anything vaguely Irish. Like Paddy Guinness. English scrum halves must have a disabling limp (usually caused by an errant New Zealand flanker), or a stupid name. "Nigel" is a good start, and some have improved upon this with ridiculous double-barreled names like Wibblington-Skrunge, Twattingly-Bottom or Wankington-Toenails
Finally, your average scrum-half is a source, off the pitch, of constant amusement. He can be relied upon to get drunk before everyone else due to his small size, will be the first to lead the singing, and have a very handy party trick involving a balloon and his penis. He will also be the one member of a touring party that will have an embarrassing and totally hilarious encounter with a prostitute and a policeman.
Hope this is of some help.
But probably not...