In the game of rugby the Kick Off and restart are the best times to put your opponent under huge pressure, with his men spread to receive the ball you have the opportunity to postition the ball in areas where he is weakest.
One tactic is to drop the ball just over the 10m line and postion 3 forwards in a triangular formation around the ball. Select the front most player to tackle. By doing this you force the opposition to make 2 gather rolls before he even gets going!
If you are using the additional Cover Defense rules, then this tactic is even more effective as the Cover defense rules will really allow you to swamp him!