Social media abuse of top tier footballers originates outside the UK in seven out of ten cases, according to data collected by the Premier League.
Overseas trolls channelling vile messages through Instagram and Twitter make up the lion's share of abusers, the research suggests.
And the international nature of the problem makes it harder for the league, clubs and UK police to tackle.
The vast majority of the culprits have no formal connection to a British club, such as membership or a season ticket, and except in the most extreme cases it may not be viable to pursue them through the law.