A linesman in Aston Villa’s game against Tottenham was hit by a smoke bomb thrown from the Tottenham supporters’ section at Villa Park.
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David Bryan, running the line in front of the Spurs fans located in the Doug Ellis Stand during the first half, was hit by the smoke bomb, which was thrown after Andros Townsend opened the scoring in the first half as Spurs won 2-0.
The restart after the 31st-minute goal was delayed by the incident but Bryan, who appeared to have been hit on the back of the neck, was able to continue.
A fan was seen being led out of the stadium by police and stewards soon afterwards.
The FA confirmed that it would investigate, while police said two men had been arrested.
An FA spokesman said: "The FA will investigate this matter, which is unacceptable. We will await the match officials' report and will be speaking to the clubs.
"Such incidents highlight the dangers of pyrotechnics being used in a football stadium."
On its Twitter account, West Midlands Police said the two men arrested were aged 25 and 47, and added: “Fortunately, the linesman wasn't injured."
Spurs boss Andre Villas-Boas condemned the incident, saying: "I think situations like this do not have a place in football. I sincerely hope it does not happen again."
The Premier League, who have issued warnings about flares this season, is also likely to investigate.
Information from the Press Association was used in this report.