Scotland's referees have warned that action must be taken to stamp down on missile-throwing at games or a match official will be seriously injured.
The body representing match officials has spoken out after two assistant referees - David McGeachie and Frank Connor - were hit with objects thrown from the Tynecastle stands during Wednesday's Edinburgh derby.
A month earlier Calum Spence suffered a wound to the back of his head after being struck by an object while running the line in front of Rangers supporters at Livingston's Tony Macaroni Arena.
Premiership official Kevin Clancy, who is chairman of the referees' association, said in a statement: "Recent incidents involving match officials being struck by objects thrown at them during SPFL fixtures are completely unacceptable and the Scottish Senior Football Referees' Association condemns them.
"Football is a passionate sport and it is that passion which makes it so special.
"Match officials, who are carrying out their duties in what should be a safe working environment, recognise that passions often run high. That is especially so at decisive moments in important matches.
"But no match official, or player, or manager, should be at risk of assault from any spectator attending a match. That is not passion, it is criminal behaviour. There have now been a series of incidents where those involved in a professional football match have been assaulted by spectators.
"The SSFRA is not only concerned about our members, but also those referees who operate at grassroots level and the message recent events may send.
"The SSFRA has a good working relationship with both the Scottish FA and the SPFL. We will raise our concerns with them, and we expect all those involved in Scottish football to work together to seek to put a stop to these unacceptable acts of violence before someone is seriously hurt."
