With regard to your question, it depends on what sort of tackle you are completing ... second phase play kills us in League ... we have trouble defending against it ... so the main object is to kill the ball and stop second phase play.
So on that basis we hit basically chest to chest in the NRL ... at levels below that we still use the shoulder.
The easiest way to for a player to find out the exact hitting area and the target area is to get the player to FIT into a tackle.
You may remember my advice on two step tackling ... I was surprised that someone thought that it was too difficult and that they wouldn't have time to do it on the field ... this is what they do on the field ...
we have just broken it down into it's individual components and coach our players in it's execution.
I recall that you are coaching a women's Rugby team ... I turned my half into a very good tackler using this method and she couldn't tackle at all before and was scared ... despite playing for 3 years.
Try it out yourself,
FIT into another player like you were tackling them ... you can then feel what the FIT feels like when making a tackle ... your shoulder will probably be in the other players guts, you back will be bent, your left leg will be beside the player and your right leg will be directly in front of them (for a RIGHT shoulder tackle) ... feel yourchest ... it is pressed against the other player.
Now bend your knees slightly ... this is the final stage of a tackle ... straighten your knees and drive up with your legs ... this is the tackle.
If you get your players feeling this FIT and practising the DRIVE, then they can analyse their own tackles on the field ... they will know if it feels right or not.
Advance your players from the FIT and DRIVE, to the last two steps.
If you are practising with another player step you left leg back one pace, step your right foot back level with your left, spread your feet shoulder width apart ... now you are at the last two steps of any tackle - the SET position.
Step forward with your right foot, crouch slightly as you step forward with your left .. you can feel the power ready to be unleashed ... your right shoulder is going back, your knees are coiled and your body weight is starting to drive into the attacker ... when you make contact ... DRIVE ... you will be surprised at how much power is unleashed.
Continue to progress your players through the tackling action ... move them back, run in, slow down for the last two steps ... stutter steps to get into position and then deliver the tackle.
Move them back further etc etc until you have them tackling on a field with an attacker moving at game speed ... anyway that's how I teach it.
But we have different defensive requirements ... although yours are changing.
I think that the term shoulder is too loose, if tacklers hit with the shoulder and keep their body out of the way, they are in danger of having the tackle broken or having their shoulder injured ... a tackle is basically a body block ... while we do hit with the shoulder and you and I both know how that is done ... if you are trying to teach players about tackling, I guess you have to go into detail or else you may have players keeping their body away from the tackle and just hitting with the shoulder.
if they hit with the point of the shoulder or hit with the shoulder but keep their body away, then they will be ineffective and probably hurt themselves ... you are probably better painting word pictures than me, but I feel that if it is an audience that are new to coaching they might focus too much on the shoulder ... the main focus (I think is on the DRIVE ... from the legs) ... if they can fit themselves to an opponent then they will be OK ... but the shoulder is the main contact point, unless you are wrapping the ball up.you have to work on it at each training session, even if only for 5 minutes.
The other thing with making a tackle is to be in the right position.
I heard the Brumbies coach on the radio today and he was talking about Rugby League defensive patterns at the breakdown.
So I guess that is the other thing that I would put into each training session (again even if only for 5 minutes) ... a drilled and disciplined defensive pattern, along Rugby League lines.
If they are starting to get the technique right, you can also start working on their talk ... get them to yell out what they are have to do ... ON THE GROUND.
A lot won't do it, but those that will yell it out, will focus the rest of the team's defence.
The attitude of the tackler in the modern game has to be spot on because of the enormous collision forces. The best exponents of the power tackle - players such as Australia's Daniel Herbert and South Africa's Henry Honiball - do not accelerate into the contact at full speed, but by the time they hit the carrier they have imparted maximum velocity through their shoulders. In essence, just before impact, they drive the shoulder through, throwing it into the attacker. This generates the impact. The next thing they do after making contact is often to lift the tackled player's leg, reducing traction, so that he's hopping and can't resist the momentum of the tackle.
Players actually need to be thinking about weight transference in the tackle, putting the power through their shoulder into the point of contact to knock back an opponent.
To demonstrate this biomechanical point, put players in pairs, one holding a contact pad, the other standing facing it. Now ask the player without the bag to root his feet on the ground adopting a wide stance, left foot parallel to right, and punch the contact pad as hard as possible. Then get the puncher to effect a 'boxing' stance (one foot in front of the other) this time emphasising the need to concentrate on transferring weight, twisting through the torso and following through with the shoulder as the punch is thrown. The power achieved is greatly increased in the second drill. It's this principle of weight transference at the point of contact which can be instilled into players by regular practice using large tackle bags. Aim to hit the bag at pace driving it upwards and backwards with maximum force.