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How will that new signing perform?

Can we predict how soccer players will perform when they switch leagues? It’s a question on the minds of many clubs’ coaches and executives during this European transfer window. A host of factors can influence the answer: playing style, role in the squad, age, adjustment to a new home, and more. Today I’ll focus on just one, league quality.

Adjusting player ratings for league quality is a critical task when using analytics for recruitment. NYA computes adjustment factors between leagues all over Europe and sometimes further afield as well. I don’t want to disclose too much about the methods, but the adjustments cover several of the ratings NYA uses to evaluate players.

It’s worth noting that the adjustment factors – at least in this case – aren’t calibrated using the historical performance of players switching leagues. Rather, they’re based on soccer fundamentals. This is to prevent the adjustments from being too backward-looking. Leagues change all the time, and basing an adjustment on the old quality of two different leagues may not be the most rational approach.

So a good test of the ratings is to see how players do after moving. Today I’m going to look at the ones who arrived in the English Premier League after making double-digit-million-pound moves last summer. By my count, there were 14 of them; please feel free to correct me on the fees if you have better information. I’ll compare how well they’re performing this season to ratings from last season – here’s the important part – adjusted to a Premier League standard. In other words, the 2014-15 ratings have been adjusted to give a best guess of how the player would have performed in the Premier League during the same season.

In the table below, I’ve listed each player along with a description of how close his adjusted composite rating from 2014-15 was to his composite rating in the Premier League so far this season. (NYA doesn’t usually use composite ratings with clients, but the detailed ratings are private.)  There’s no adjustment for the difference in quality between the player’s old and new teams, though some controls for team quality are already baked into the basic ratings. And there’s no discount for the possibility of playing a new position, being homesick, disliking the coach, failing to learn the language, getting older, or anything like that.

For half of the players, the adjusted ratings for 2014-15 came within 5 points on a 0-100 scale of the actual ratings for the current season. I marked each of these as a “HIT”.  For a difference of 6 to 15 points, I said it was “CLOSE”. And where there was a difference of more than 15 points, I said it was a “MISS”.

The good news is that 10 out of 14 adjustments were hits or close ones. All the closes ones and misses were to the downside. This isn’t surprising, since some players may need time to adapt to their new situation. Adaptation is a temporary drag on performance, though. There are plenty of other things that can really make a transfer go wrong.

For example, take Manchester United’s four big-money signings – only Anthony Martial was a hit. This may give ammunition to those who accuse Louis van Gaal of squandering the club’s costly talent. Certainly none of the players who arrived over the summer had played such a defensively focused, stifling style before coming to England.


But other factors may also be at work. Schweinsteiger, for one, might have fallen off the end of the aging curve. Down in London, Pedro left one of the best teams ever to play professional football to join the Chelsea implosion. Newcastle may also have failed to get the most out of its signings; Wijnaldum and Thauvin joined a club that had a fairly dysfunctional setup for much of the season. Soccer is a team game, and even Lionel Messi probably wouldn’t be as much of a world-beater on the Tyne these days. Also, Thauvin is not Messi.

There are several lessons here. First, new signings almost never perform better than a model based purely on performances and league quality would predict; the risks are mainly to the downside, and they may not be solely related to aging. Second, players joining a struggling team may have a hard time shining as brightly; one or two players can’t rescue a failing system by themselves. And third, when so much money is at stake – more than £300 million just from these players – it’s worth a lot to ensure that the adaptation process goes quickly and smoothly. Otherwise, you might as well have used that cash to fertilize the pitch.