Strength and height are an important attribute to any lock player. Within the scrum their strength is important to work against their opponents push forward and also to drive their own scrum forward when attacking. They help to back up the front row and provide extra support for them.
Their height is an advantage in the line outs as their main role here is to win the ball, or at least make it difficult for their opponents to take a clean catch.
In open play the locks should be prepared to get involved with the rucks and mauls, ripping out any loose ball from them. Help out in both attacking and defensive situations, tackle any opposing ball carrier close to them. They should also attempt to catch or grab the ball from kick off.
The most common way for locks to bind in the scrum is to wrap the arm closest to the other player around their back to the outside hip. To join with the front row they place their outside shoulder into the buttock of the prop on their side, leaving enough space for the hooker to play the ball back. Then reach round as far as possible with the outside arm towards the props hip.
When pushing in the scrum the movement comes from extending the legs, and taking short, quick steps to gain a good grip on the ground as soon as possible. However if the opponents are pushing, it is important to try and keep all studs in contact with the ground to improve grip.
In the line out situation the lock, should start with a wide stance and look ready to receive the ball even if they know it is not coming to them. However if the lock is receiving as signaled by the leader of the forwards, they need to jump up and slightly forward. As they catch the ball at the top of the jump they should bring it into their chest, then turn so they have their back to the opposition. If locks don't feel confident about catching the ball they can tap it down to 1 of their teammates.