Premier League and squad depth: Is rotation really an issue for Liverpool, Man City & Co.?

Death, taxes, and Antonio Conte complaining about his lack of squad depth: These are the three constants of life in the 21st Century.

In January 2018, during his final season with Chelsea, the Italian manager said: "I don't know what will happen at the end of this window. The club knows my thoughts about this. If we stay with these players, then I am very happy, too. I think we just need to improve the numbers, because in some roles we are missing a few players."

This past November, Conte wasn't quite as passive-aggressive. After a loss to Borussia Dortmund in the Champions League just a couple of months into his first season with Inter Milan, the irascible boss went off. "Apart from Diego Godin, these players haven't won anything and lack experience. We have too limited a squad to face both Serie A and Champions League football this season. I mean limited in terms of numbers and quality. Some players have to be on the field constantly, and in the long run, you do pay for that. I am furious because this cancels out the good work."

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Ignore the questionable morale management behind such pleas: I need new players because the players I work with every day aren't very good! Please forget that Chelsea and Inter are two of the 15 richest clubs in the world and instead focus on this: The last time he won a league title, Conte did it without much depth at all.

In 2016-17, Chelsea won the league with 93 points, the second most in club history, and they did it by playing the same players over and over and over again. Only 13 players featured for more than 600 minutes in the Premier League. For comparison, Jose Mourinho's Manchester United used 21 players for at least 600 minutes and 19 of them for at least 1,200. They finished sixth.

"That's a very settled squad when you consider that a Premier League season usually involves 3,600-plus minutes," said Dan Altman, creator of the analytics website smarterscout.com. "Of course, Chelsea had finished 10th in the previous season and were out of European competition."

With the FA Cup kicking into gear, the Champions League/Europa League knockout rounds coming soon and the January transfer window open for another week or so, "squad depth" is the buzz-phrase of the moment.

Who has the rosters to weather the increasingly crowded fixture lists, the inevitable injuries and the unexpected yellow/red card suspensions? However, despite Conte's constant fretting, the last non-Manchester City team to win the Premier League -- his team -- did it with a tied-tight group of key contributors. Not everyone needs squad depth, and, in fact, sometimes you can have too much of it.

"Squad depth is obviously an important insurance policy against injuries, but the importance of squad depth depends mainly on the number of competitions in which the club is involved," said Altman, who was also formerly senior adviser for football operations at Swansea City. "It's impossible for a club playing in a domestic league and three cups to play the same starting 11 every day. Players will get run down quickly and be running on fumes by the end of the season."

According to analysis from the consultancy 21st Club, Premier League clubs that play in Europe typically need 20 players who can play at least 900 minutes across all competitions. Those that don't? They require, on average, only 17.6 players to reach the 900-minute threshold. Think of it this way: If your team qualifies for Europe, you're going to need 2.5 extra contributors in your squad compared to before.

Even in this regard, Conte's title-winning Chelsea are unique. Add in the EFL Cup and the FA Cup, and the only players to break 900 minutes were those same aforementioned 13. The same goes for the previous season's title winners, Leicester City. They didn't play in Europe, and like his fellow countryman, Claudio Ranieri cut down his squad to an extreme degree, with only 14 players breaking that 900-minute barrier. Manchester City, meanwhile, racked up the two highest point totals in Premier League history in each of the past two seasons, but their squad usage looked much closer to average. With Champions League games to contend with, Pep Guardiola deployed 20 players for at least 900 minutes in 2017-18 and then 21 last year.

Liverpool, however, serve as a more intriguing example.

In 2017-18, when the Reds finished fourth and reached the Champions League final, Jurgen Klopp deployed 19 different players for at least 900 minutes. Last year, which followed the shortened World Cup summer and the extended 2017-18 campaign, they improved by 22 points and won the Champions League, but Klopp gave only 900 minutes of playing time to 16 players -- or fewer than the average Premier League team that doesn't qualify for Europe, let alone one that makes it all the way to the Champions League final. This season, thanks to added games and added time in both the UEFA Super Cup and the Club World Cup, Liverpool have already had 16 players break 900 minutes. But when you're 16 points up with 16 games to play, squad depth becomes a moot point.

Depth, then, might be important, but not as important as being able to continually rely on your best players. At least, that's the gist of some of the work done by Laurie Shaw, a former astrophysicist who's now a research fellow at Harvard University.

"The general conclusion was that teams that the majority of teams that prioritized stability and a small playing squad all had successful seasons by their own standards," said Shaw, "while those that rotated frequently had a disappointing year in terms of league performance."

Of course, player usage isn't totally up to the manager. If someone gets hurt or suspended, you can't keep rolling them out there, and the same goes for players who leave on loan or on a permanent basis during the January window. Other players will tire in ways we can't see from the outside, and sometimes, the playing time balance has as much to do with keeping people happy as it does with maximizing your chances to win every game.

"Ultimately, it looks like bad management if a team -- particularly one with plenty of resources -- doesn't have sufficient cover to cope with injuries to key players, especially if those players have recently been injured, or are known to be injury prone," Shaw said. "On the other hand, buying players purely to increase squad depth when there are no real injury concerns could backfire if it disrupts a settled team."

Other research from 21st Club has shown that managers are more likely to change their teams if they lose matches even if the underlying performance suggests they were just unlucky. "A large squad might be more difficult to manage, and it increases the temptation of tinkering with the starting lineup," Shaw said. This, specifically, seems like it has been a bit of a problem for Frank Lampard in his first season with Chelsea.

At the beginning of the 2019-20 campaign, Lampard had settled on a lineup that included Tammy Abraham, Willian and Christian Pulisic up top, some combination of Mason Mount, N'Golo Kante, Jorginho and Mateo Kovacic in midfield, and Emerson, Kurt Zouma, Fikayo Tomori and Cesar Azpilicueta across the backline. After a rough stretch in late November and early December, in which the team won one and lost four despite edging opponents on expected goals (8.2 to 5.4), he has shuffled in and out of a number of different lineups, and the results and the underlying performances have both suffered.

Among other Premier League teams this season, Sheffield United stand out for their player-use patterns.

"Sheffield United have nine players with 1,700-plus minutes at a position already, and four strikers who've split the other two spots," Altman said. "It's remarkable, and possibly part of their success. These players are used to working with each other in the same system. The question is how long they can keep it up without exhausting themselves." The other question: What happens if Chris Wilder & Co., currently in seventh, qualify for Europe next season?

Both Manchester clubs have the opposite problem, as they've each dealt with injuries at opposite ends of the pitch. "Man United appear to have insufficient cover for their first-choice forwards, and Man City have insufficient cover in central defense," Shaw said. "I haven't attempted any kind of quantitative analysis on this, but I think it's reasonable to say that the lack of cover has cost both teams goals and points this season."

After Marcus Rashford suffered a serious back injury over the weekend, United have only one prime-age player with high-level experience, Anthony Martial, to play across their front line. That kind of wild resource mismanagement, though, is in keeping with the way United have done things for the past decade. The line between too little and too much depth is a thin one, and the Red Devils have failed to straddle it. They had Romelu Lukaku and Alexis Sanchez last season, but now both of them are in Italy ... playing for Antonio Conte.