IF LAST year’s Brexit vote was many things, it was assuredly not an endorsement of a surge in economic migration from South Africa. Yet in cricket, that is what has transpired. This winter six South African players have used a European Union law to join English county cricket teams, a case study of Brexit’s impact in unforeseen areas.

In 2000 Maros Kolpak, a Slovakian handball player, was released from his German club because of a limit on non-EU players. (Slovakia had not yet joined the union.) Mr Kolpak complained and, in 2003, won a case at the European Court of Justice. This granted immunity from such quotas to anyone from a country with an EU association agreement that included non-discrimination clauses. Among these is South Africa.

In sports with limits on foreign players, the Kolpak law provides a handy loophole. Only two foreigners per team are allowed in English rugby’s top flight, for instance, yet 72 Kolpak players appeared over the last rugby season.

In County Championship cricket, which has a limit of one foreigner per team, there are far fewer Kolpaks—only 12 last season. But there has been an upswing since the vote to leave the EU. “Players are taking the opportunity because they think that Brexit may close it down,” says Tony Irish, chief executive of the South Africa Cricketers’ Association. Whereas rugby has numerous professional leagues in Europe, England has the only lucrative cricket competition. South African players have also been nudged to move by the long-term slide of the rand, as well as by racial quotas at home (the latest Kolpak migrants are all white).

Players are able to sign multi-year contracts that will last beyond Brexit. Yet they may still have to leave after Britain departs the EU, says Borja García of Loughborough University. He foresees conflicts between players, clubs, governing bodies and the Home Office. It is a corridor of uncertainty.

The debate about the merits of Kolpaks in cricket resembles that about migrant workers more generally. Some think that the influx of foreigners deprives young English players of opportunities. But there is also recognition that they raise standards.

In South Africa, feelings are less ambiguous. Fury about the exodus is compounded by the clandestine nature of departures. Rilee Rossouw, a batsman in the national squad, informed the team by e-mail while misspelling the coach’s name. Kolpaks must renounce the right to play for their country, so South Africa faces touring England next summer shorn of several important players—and worried that others could use the trip to secure a Kolpak contract of their own.