When Charlton Athletic's Keith Peacock walked onto the pitch wearing the Number 12 shirt on 21st August 1965, the first ever substitute in English football can’t have known he would play a part in changing the beautiful game forever.

If Jean-Marc Bosman’s contract dispute created an inadvertent watershed that would see player power rise exponentially over the subsequent decades, then Peacock, even more inadvertently, provided the spark for a team game becoming a squad game, for managers earning their reputations from not only how they constructed their sides and upon which principles but also how they could tactically manipulate matches with the astute use of substitutions.

Keith Peacock with Scott Parker

Initially, after being sanctioned for the 1965/66 season, each team was allowed just one substitute who could only be brought on for an injured player. But as Don Revie and Leeds quickly became notorious for suspicious injuries usually around the 70th minute mark, a defender when losing and a forward when protecting a lead, just two years later it was agreed substitutes could be used for any reason. At that moment, squad era of English football went into full swing.

Fast forward 51 years and managers are now privy to three substitutions from a bench of seven, four even for extra time in some cup competitions. As it has in so many aspects of English football, the conception of the Premier League boasts its own transformative impact on the substitute timeline; it was a year ahead of the Football League when introducing three substitutes in 1992/93, and by 1996/97 had already boosted the bench up to five. Since 2008/09, Premier League managers have been luxury to seven.

And nowhere in world football right now is that privilege being exploited and maximised more than at the top end of the Premier League. While there’s little benefit in merely tallying up the number of substitutions made, so customary has taking advantage of all three become, their impact on games this season is incredibly revealing.

Goals and Assists from the bench - Big Six

First and foremost, a simple fact tells much about this term, which is fast-becoming the season of the supersub: in just twelve games, Arsenal, Liverpool and Tottenham have recorded as many Premier League goals from substitutes as they managed throughout the entirety of 2017/18. Barring Manchester City, in fact, every member of the Big Six owes a greater percentage of their Premier League goals for 2018/19 to substitutes than they did at the end of last season.

But the influence of substitutes stretches far beyond the immediate scoring tally. Comparing the opening dozen games of 2018/19 to last season, the Big Six have scored three extra goals and perhaps more significantly conceded eight less after making their first substitution, seeing their combined post-first-sub goal difference jump up from +36 to +47.

Goals after substitutions - Goal Difference

In the process, four of the six teams have improved their post-first-sub goal difference by an average of 8.5, the only decreases being from Manchester United - who are enduring a frankly terrible season - and Manchester City, who have a habit of seeing off games before the point when substitutions are needed.

Tellingly too, the average time of the first substitute has dropped from the 63rd to the 59th minute, and the collective percentage of goals scored after the opening substitution has risen while the percentage of goals conceded has fallen. In fact, every Big Six side has conceded a smaller percentage of goals than in the first twelve games of last season, while an incredible 69% of Arsenal’s goals and a whopping 55% of Chelsea’s have come after the manager’s first change.

Goal Impact of First Substitution - Big Six

The overall percentage of goals scored by substitutes amongst the Big Six has shot up from 9% to 16%, and the average number of goals by substitutes per game has risen from 0.18 throughout the whole of last season to 0.33 at the start of this term. Clearly, substitutions are generally being made earlier this year and to far greater effect.

Of course, there are mitigating factors here, particularly regarding Arsenal whose post-first-sub goal difference has completely transformed from -1 to +15. A big chunk of that is owed to Pierre-Emerick Aubameyang, who has the second-most substitute goals of any player in Europe's top five leagues.

But whereas there were no new managers amongst the Premier League’s Big Six at the start of last term, the Gunners and Chelsea have both implemented a changing of the guard and Unai Emery and Maurizio Sarri respectively are still working out which personnel are best-suited to various opposition, making early and recurring changes from the bench somewhat inevitable.

Percentage of goals scored by substitutes - Big Six

It’s become a curious quirk of Arsenal’s season that despite enjoying a ten-game unbeaten run in the top flight they’re still yet to be leading a Premier League game at half time under the Spaniard. Every win has required in-game tinkering and reshuffles, and Sarri too has relied heavily on his bench to get his Chelsea side over the line - often switching between Alvaro Morata and Olivier Giroud to change the dynamics of his attack.

But that in itself is testament to what makes the top of the Premier League so spectacular right now. While the Premier League may lack an undisputed flagship entity like Lionel Messi, Cristiano Ronaldo or Neymar - although some would argue Eden Hazard has now reached that level too - the real quality stems from the managers.

Average minute of first substitution

Jose Mourinho and Pep Guardiola represent the greatest managerial rivalry of their generation, in terms of intensity, diversity and trophies, Jurgen Klopp has won Bundesliga titles and reached three European finals, Unai Emery’s CV boasts three Europa League titles and Maurizio Sarri and Mauricio Pochettino make up in enthralling style of play and team development for what they currently lack in silverware.

The Big Six are blessed with managers who have the talent to consistently and effectively change games using the bench, but that’s also a consequence of possessing the right quality of squad in the first place, and how the clubs at the very top of the table have steadily outgrown the rest of the league.

The gap may not seem as large as last season when the Premier League finished with nine points between sixth and seventh and a further five between sixth and eighth, but in terms of squad depth the chasm is certainly still there. Last season, Big Six clubs were responsible for 38% of all substitute goals - this season, that return has increased by more than a third to 60%. And whereas the Big Six are averaging 0.33 substitute goals per match this season, the rest of the division is managing just 0.09.

Changes in impact of subs - Big Six

Yet, while we can hone in on a narrative that encompasses the recent allegations over intentions to create a European Super League, it's important to look at the bigger picture here. In the space just over half a century, the beautiful game has transformed from begrudgingly allowing one injury replacement out of sheer necessity to a top team owing 69% of its goals to how their manager has changed the game with the use of three substitutes, chosen from a raft of seven.

When Peacock observed the opening whistle awkwardly from the touchline at Bolton Wanderers, wearing the number 12 shirt, on the first Saturday the 1965/66 season, he can't have imagined his introduction for Mike Rose just 11 minutes later would go on to have such an ever-lasting effect on football, tactics and managers - the full extremities of which, we have by no means yet reached.

For the first time ever, the World Cup accepted a fourth substitute in extra time last summer. Who knows what the next chapter will be in the constantly evolving story of the substitution.

Watch Playmaker FC's Thogden react to England's dramatic second-half comeback against Croatia in the video below...