Defend outnumbered without being pulled apart, then punish. Stay compact, deny the pass inside, press the ball with cover behind, and the instant you win it, look up and hit the empty net.
The attacking team has an extra player and an empty net behind them; the defending team is a man down. Defend compact in a mid-block, keep the ball away from your goal, press the ball with close cover and deny the pass inside. The moment you intercept, look up and shoot at the empty net or carry it away and finish. Rotate which team is outnumbered.
With the goalkeeper pushed up as an outfield player, the net behind the attacking team is empty. That single fact should shape everything about how the power play is defended, because it means the reward for one clean turnover is not a counter-attack. It is a goal, from almost anywhere on the court, into an unguarded net.
So the block has to be built to win the ball cleanly rather than merely to survive. Blocking a shot out for a corner keeps the score level and hands possession straight back. Intercepting a pass ends the possession and very often ends the game.
Compactness comes first. Five attackers with a spare man will move the ball around a block patiently, hunting one pass inside, and the instant that pass is completed the shape is broken and somebody has a free shot. Deny the ball inside and accept that they will keep it. Letting the opposition pass sideways for thirty seconds is a defensive success in this situation, not a failure.
Keep the block high enough that shots come from distance. Sitting on the goal line concedes the entire court and eventually somebody arrives unmarked at the back post. One player presses the ball, the nearest covers behind him, and nobody else leaves the block to join in.
The hardest part is patience and it is worth naming before you start. Being outnumbered is uncomfortable and the instinct is to go and win it back. Every player who breaks the block to chase creates exactly the gap the fifth attacker was added to occupy.
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.