The grubber:key factors:
If running , slow down to balance yourself;
Lean forward, head and eyes over the ball
hold ball upright hands on each side
release ball and make contact just before it lands
point toes towards ground
contact ball with top of foot(laces of boot area)
keep knee bent and ahead of the balls
hit the top half of the ball to make it go end over end
follow through with low straight leg
Basically it is a stab kick at the ball and is used to put the ball in behind them or as I tell my players.... you are going for the gap and it closes and you think I can't make it....but the ball can.
If your players have trouble with the kicking foot, they can side foot the ball instead of using the top of their foot ,i.e. hit it with their instep like a soccer player passing a ball.
I make my players run along the lines of the field and use the lines to kick the ball along, trying to use the cross lines as a guide for how hard to kick the balli.e. start on goaline run along sideline and grubber to 22m line ,pick up ball and grubber to 10m line , to half , to far 10m to far 22m to goaline ,so they get a few grubbers of varying lengths to kick and learn how hard to kick the ball.
You can also put them in 3s and use a relay format to get volume..1kicks to 2 and follows 2 kicks back to 3 and follows 3 kicks to 1 and follows..