Legs That Have Not Grown, and the Trap Called Five Substitutions

Three in the afternoon, and the training ground of Incheon United was empty as a blank page. Just me and a seventeen-year-old boy named Park Ji-hoon, a full head shorter than his teammates. On my wrist were two old stopwatches: one counting the rhythm of his running, one counting the rhythm of his breathing. He started, and the needle stopped at 3.9 seconds for thirty metres. Not one person on the coaching staff turned to look. But I looked, because I am the one who records rhythm. People record goals; I record rhythm. Neither ever repeats itself.

I followed him for three months, noting every session, every touch, every time he was shouted at until his face went red. In that notebook there is one line I wrote over and over: "He runs faster than his age." Back then I thought it was a compliment. Now, after nearly fifty years in and around football pitches, I understand it was a warning.

The training ground is empty; I open the old diary, and I am seventeen again.

The story of Park Ji-hoon is not about Park Ji-hoon. It is about a change the football world quietly accepted a few years ago: five substitutions. In May 2026, amid the panic of the pandemic, the International Football Association Board (IFAB) temporarily approved five substitutions per match instead of three. The stated reason was humane: congested calendars, exhausted players, a need to protect their health. By the 2026-2026 season, the temporary measure became permanent.

Everyone nodded along. Coaches liked it, because squads ran deeper and rotation came easier. Analysts praised it, because young players got more chances. I sat in the stands, listening to the applause, and thought of the boy in Incheon. Because there is one thing nobody measures: rhythm. Nobody counts whether those legs have grown enough before they are thrown into the rhythm of grown men.

Incheon taught me to watch a match with my ears first, and my eyes second. And my ears hear what the eye skips over: the breathing of a young player in the seventieth minute, when his lungs have never been trained to endure seventy minutes like that.

At seventeen, a player is still inside what physiologists call a "growth window". The bones have not closed, the growth plates are still soft, the neuromuscular system has not yet perfected its control of force. A boy can run thirty metres in 3.9 seconds, but that 3.9 seconds is paid for by a body not ready for a game every three days. I wrote this down in my notebook: at the same speed, Park Ji-hoon's recovery rhythm after every heavy session ran twenty minutes longer than his teammates'. Nobody saw it. Nobody measured it. Because we only measure what happens during the match, never what happens afterwards.

This is the biggest blind spot of modern football: we optimise for the moment of brilliance, but forget the recovery rhythm that stands behind it. A young player is sent on in the sixty-fifth minute, sprints flat out for the last thirty, scores once, is celebrated. In the stands, people see a new talent. In the recovery room, people see a body that needs two extra days to come back. And when the calendar thickens — the very problem five substitutions were born to solve — it is the young players who are pushed into the mill the hardest, because they are cheap, they are obedient, and they do not yet know how to say "no".

I once thought five substitutions were a gift to attacking football. They are. But the gift comes with a trap: it turns the final twenty minutes into a war of attrition, where the side with the fresher pieces wins. And the freshest, cheapest, most easily spent piece is usually an eighteen-year-old boy.

I have an odd habit: I count how many times a young midfielder turns his head toward the touchline before receiving the ball. In a mature player, that number is stable. In a young player, it swings wildly — the sign of a nervous system still learning to process information, not one that has mastered it. When you push a learning brain into the tempo of a mastered brain, you do not teach it to go faster; you teach it to be afraid. And fear never made a great footballer.

What few notice lies in the data. Across Europe's top domestic leagues, the total minutes played by players under twenty have risen sharply since five substitutions became common. That sounds good. But isolate the group under eighteen and a different pattern appears: their average minutes per appearance fall, while their frequency of appearance rises. In other words, they are not given more time to grow within a match; they are broken into shorter fragments, and used more often. That is the difference between nurturing and consuming.

There is a way to see this without a laboratory. Look at the minutes a young player plays over three consecutive months, then compare them with the next three. If the curve climbs without a single pause, that is not maturity. That is a red flag. The human body does not grow in a straight line; it grows in rhythm — load, rest, load, rest. Take away the rests and you do not accelerate the growth, you only shorten how long it survives.

I remember the 2026 World Cup. While my colleagues poured all their attention into our national team's match, I sat counting Kevin De Bruyne's off-ball movements. Forty-seven times in a single game, he created space for a teammate without the ball ever reaching his feet. Nobody recorded it. Because we only record what ends in a shot. The 2026 World Cup: I got lost in a forest of data, and found a legend — in the things that are not counted.

That taught me a lesson about youth development: the things that decide a player's career rarely appear on the scoreboard. The growth of a pair of legs is not in the number of goals, but in the number of rest days. And rest days cannot be sold. Nobody sells a ticket to an afternoon in which a boy sits on a chair, watching his teammates train, so that a knee can heal.

There is a misunderstanding I meet again and again. People say: "Play him a lot and he'll grow." I have heard that line for forty-nine years, and it is always half right. The other half is buried in injuries nobody wants to name. I have seen too many players who shone at nineteen, fought their knees at twenty-two, and sat on the bench of a lower-division club at twenty-five. Football's memory is short. People remember the shot in the eighty-eighth minute, not the surgery of a Tuesday morning.

And here is the irony: the very system designed to protect players is quietly pushing the youngest into the most dangerous place. Five substitutions are not inherently bad. They merely expose an old habit: we always choose the cheap, the fast, the immediately visible. A coach under pressure to get results will send a seventeen-year-old on in the seventieth minute, because those legs are still fresh. He has no time to wonder how those legs will be in December.

I count every stride on the training ground, but what I remember is the coach's sigh. That sigh is not for the result. It is for a boy he knows he is using the wrong way, and cannot do otherwise, because next week there is another match.

If you ask me for a solution, I will not give you a list. I will only tell you an old habit of mine. Whenever I write about a young player, I always fill in one extra box in the notebook: "Most recent rest day." Not goals. Not minutes. The rest day. If that box is empty, I know I am reading about a player being consumed, not one being nurtured.

Football will not stop to wait for a pair of legs to grow. But a mature football culture must know that some things cannot be accelerated. I have sat in Incheon long enough to understand: rhythm waits for no one, but legs have the right to be waited for. The question I leave with you, reading these lines on an empty afternoon: when did you last count a young player's rest days?