PITSEA, England—The great names of English soccer ring with the echoes of Britain’s industrial past—Liverpool’s docks, the railway works that gave birth to Manchester United, the foundries that built West Ham.

Then there’s Hashtag United.

The club sprang to life through a group of friends led by Spencer Owen, who played video soccer games and streamed them online. He built a large following on YouTube, and now Mr. Owen and his brother have turned their digital team into a real-life soccer team that’s climbing up through England’s semipro leagues—and slowly winning over rival fans who questioned their bona fides.