Transition for beginners: the moment the ball changes hands, react. Win it and go forward immediately, lose it and sprint back. The first two seconds decide the outcome.
Mark a 50x35m area with a full goal and keeper at one end and a mini goal at the other. Two attackers start with the ball against one defender. If the attackers score, they go again. If the defender wins it, at that moment he attacks the mini goal and the two attackers must recover and stop him. Rotate roles constantly. For younger groups, shout a cue word the moment possession changes so they learn to connect the word to the reaction, then take the cue away once they are reading it themselves. Judge the repetition on how fast everyone reacted, not on whether it was scored.
Young players treat attacker and defender as identities rather than as jobs that swap. Ask a nine-year-old what position he plays and he will tell you what he is, not what he does, and that is the real obstacle to teaching transition. The problem is not effort or fitness. A player who believes he is a defender does not look forward when his team wins the ball, and a player who believes he is a striker does not sprint back when they lose it.
So the concept here is narrow and worth stating plainly to the players themselves: the instant the ball changes hands, everybody's job changes at the same moment. Not just the nearest player, and not after a look around. Everybody, immediately.
Winning it and looking forward first is the attacking half. Young players who win the ball tend to look sideways or backwards because those passes feel safer, and by the time one has been played the opposition has recovered its shape. Looking forward first does not mean playing forward every time, but it has to be where the eyes go before anything else.
Losing it and sprinting back is the half that gets neglected, because it is unrewarding. The nearest player presses to slow the ball down, everybody else runs. Neither of those produces anything visible, and together they decide whether the next thirty seconds happen in your half or theirs.
Two seconds is the entire coaching window. React inside it and the numbers favour you. React outside it and the game has already moved on without you.
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.