Defend a long throw into the box. Attack the ball, be first to the contact, and head it clear high and wide before the attackers can flick it on.
The opponent takes a long throw into the box. The key defender attacks the ball and heads it clear, high and wide, winning the first contact before the attackers flick it on. Emphasise attacking the ball and not letting it bounce. Add markers and a keeper command as a progression. Rotate the roles.
Long throws score from the second contact, almost never the first. Nobody heads a throw-in directly into the net. What happens is a flick at the near post and a body arriving behind it to turn that flick over the line, and it is the two-stage threat that makes the delivery worth defending properly.
So the defensive priority is the first contact, and it has to be won early and high rather than waited for. A defender who sits off and lets the ball bounce has surrendered the only moment he controls. Once it is flicked, the ball is behind a line of defenders, travelling away from the keeper, into a crowd nobody is watching.
Attack it at its highest point. That is not a technical nicety, it is about who reaches the ball first when both players are jumping from a standing start. The defender who takes off late is beaten before the ball arrives.
Head it high and wide. High buys the seconds the team needs to push out, and wide takes the ball out of the corridor in front of goal. A clearance headed straight back down the middle at chest height is simply a second attack, and it is the most common error at this restart.
Two things worth arranging before the throw is taken. Put a defender on the near post, because that is where the flick is aimed and an unoccupied near post is the whole reason the routine exists. And push the line out the instant it is cleared, because the throwing team has committed bodies forward and is badly balanced.
Save it to your private drills, then change the animation, adjust positions, swap equipment, or drop it into a session block. Or start from a blank pitch and build your own.