In the modern game, the flankers are two of the most important players on the pitch.
Basically, the job involves following the ball around the park.
When the backs take the ball in, it's your job to win the ball back for your team.
It also involves taking the ball into contact yourself and making as many yards as possible with the ball in hand.
Lewis Moody facts
Born: 12 June 1978, Ascot
Club: Leicester Tigers
Height: 6ft 4ins
Weight: 16st 6lbs
And of course the defensive side of your game is crucial.
You should be hunting down the opposition whenever they have the ball and putting in big hits.
You've got to be confident and strong in your tackling.
And if you can offer an extra option in the line-out then all the better.
So you need pace, power and agility to be a flanker.
But the most important quality of all is enthusiasm - you really have to want to run around all day and do the hard work.
Getting your mind right
Before you play you have to get yourself in the right frame of mind.
If you're not mentally right, you won't be able to produce your best on the pitch.
The way I prepare for a game is by visualising in my head what it is I want to do in the game - make 100 yards, score two tries, don't miss any tackles - and imagine it all happening.
I sit down for a few moments to think about these things and then I'm bouncing off the walls like an idiot!
I try to go out before kick-off with a couple of other guys to do some sprints and get the feel of the ball in my hands - that's really important for me.
Everyone's different though - you have to do what works for you.
Danny Grewcock has a good wander before a game
Some guys run around shouting and screaming whereas others prefer to chill out and read a book or something like that.
For instance, my England team-mate Danny Grewcock wanders around the pitch with a ball on his own.
He walks to every corner of the pitch and re-enacts what he might do in that area during the game - very strange!
Josh Kronfeld, my former Leicester team-mate, cracked me up the first time I saw his preparations.
He was doing some kind of old-school disco dance with his arms and legs going everywhere like John Travolta!
I definitely lost my focus before that game!
For some players, superstition is very important.
Lucky underwear, lucky socks, turning the lights on and off, being last out of the changing room - it all goes on.
But it's not that important for me - I don't have any lucky pants!
But one thing I do have to do on the night before a game is go to the cinema - I see it as part of my routine rather than a superstition though.
Whether it's for club or country I always go to the cinema and I try to get a 'try-jam' out of it.
A try-jam is our celebration if one of us scores a try the next day.
And we base it on the film that we've watched!