Set up 4 cones about 5 yards apart in all directions.

B is the ball carrier.
O is the offensive player/blocker.
D is the Defender or the tackler.

D will attempt to tackle or place 2 hands on the ball carrier.

O will block D until the whistle blows or D touches the ball carrier.

Ball carrier must not leave the square, however can move to set up his block from O or to stay behind O.

Watch for holding by the offensive player,

Make sure to teach proper position when blocking.
Back straight, head up, form fit position.

Defenders can do anything they need to do to get to ball carrier

Ball carrier, tries to use and set up all his blocks.