Running back LeGarrette Blount #29 of the New England Patriots rushes the football in the first quarter during the NFL game against the Arizona Cardinals on September 11, 2016 in Glendale, Arizona Christian Petersen/Getty Images

ESPN's Fantasy Football app and site went down on the first Sunday of the National Football League (NFL) season for hours, leaving millions of irate fans in the dark as the regular season kicked off on 11 September. Numerous enraged American ESPN Fantasy Football players, including a US senator, took to social media to voice their frustration and complaints about the outage that left them unable to check on their fantasy team rosters and up-to-the-minute scores.

Users reported receiving an error message stating: "There was an error while trying to reach Fantasy Football. Please try again."

ESPN Fantasy Sports acknowledged the interruption about an hour after kickoff at 11 am PT in a series of tweets on its official Twitter account saying that it was aware of the issue and was working to correct it.

The downtime expectedly sparked a wave of criticism from disappointed fans on social media, particularly since the outage occurred on the first day of the season.

US Senator Claire McCaskill from Missouri also tweeted about her own disappointment at the outage.

ESPN later confirmed that its Fantasy arm's service was restored and apologised for the intermittent outage. It added that they "identified a backend data access issue" that was quickly resolved. However, they noted that the issue "did not impact data for teams, leagues or rosters".

Touting itself as the most widely used fantasy football site in the US, the ESPN Fantasy football platform experienced an outage during opening week back in 2014 as well while Yahoo's final fantasy football website , the country's second most popular fantasy site, suffered a similar outage after the app crashed during game time on the first day of the season in 2013.

The number of people participating in fantasy sports in the United States and Canada has exploded over the years, leaping from just 500,000 in 1988 to more than 57 million people in 2015, according to the Fantasy Sports Trade Association. Fantasy sports players spend an average of $556 on league-related costs, materials and single-player challenge games over a 12-month period while some zealous players make six-figures betting on fantasy football.

According to comScore data, ESPN set a sports category record in 2015 with ESPN Fantasy Football helping drive its unique user count to more than 94.4 million in the US.