Have students positioned along a line with their hockey sticks sleeping and facing the coach to observe a brief explanation/demonstration of how a tackle is made correctly. 

1) in haka position the defender will get close enough to player that has possession of hockey ball
2) defender will remove hand at bottom of grip to maximise reach by leaving hand on at the top of grip
3) students will now picture hockey stick like a "snake tongue" as it shoots out of its mouth at a high speed to catch prey by pulling it back toward mouth. The stick will move in a similar manner as it will reach out quickly, wrap the hook round hockey ball and move back toward body. 

Have students practise this without a ball and move along the line observing students execute properly by removing the correct hand (bottom) from stick. Once students have mastered this, they can then move into game.