Two men were arrested after an assistant referee was struck by a flare thrown from the stands during Tottenham Hotspur's 2-0 Premier League win at Aston Villa on Sunday.
Spurs had just taken a 31st-minute lead through Andros Townsend at Villa Park when a canister trailing black smoke was lobbed towards the playing surface, apparently from the away supporters' section.
It hit assistant referee David Bryan on the back, causing him to stumble forwards, but after a brief stoppage in play while referee Phil Dowd spoke to his colleague, the game continued.
Local police revealed that two men had been arrested in relation to the incident.
"Police have arrested 2 men after a lit flare was thrown on the pitch during the Villa v Spurs game - the flare hit a linesman," said a statement from West Midlands Police published on Twitter.
"The two men aged 25 and 47 were arrested following the incident at Villa Park, fortunately the linesman wasn't injured."
Later Sunday, the Football Association said that the incident would be investigated.
"The FA will investigate this matter, which is unacceptable," said a spokesman.
"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."