The Football Association is to investigate after bottles were thrown at an official during Millwall's FA Cup home win over Aston Villa.
Referee Neil Swarbrick delayed play in the second half when plastic bottles were aimed at assistant Mark Scholes.
"We will be looking into it. We are waiting the referee's report plus details from an FA crowd advisor who was present," said an FA spokesman.
Millwall won Friday night's fourth-round tie
2-1 at the Den
The Championship club knocked out their Premier League opponents thanks to John Marquis's 89th-minute header.
Bottles were thrown at Scholes after a foul was awarded against the hosts. Police made three arrests at the game.
Millwall manager Kenny Jackett said: "We can't condone people throwing bottles on to the pitch. That doesn't help us.
"There's a line between supporting your club and creating a passionate atmosphere but we don't want to step over that line."