Aston Villa manager Steve Bruce criticised Birmingham's decision to give their supporters cardboard clappers for the Championship derby at St Andrew's on Sunday.
Some home fans threw the clappers at Villa players including Robert Snodgrass during the 0-0 draw and Bruce was far from impressed.
Bruce, a former Birmingham boss, said: "Whoever made the ridiculous decision to have clappers here obviously doesn't know the Birmingham-Villa game as the Birmingham fans don't need a clapper. It is the last thing they need.
"But they have somehow used them as a weapon. In all seriousness someone could have been badly hurt.
"They were rolled up, elastic bands around them, and they became like a rock.
"Thankfully no-one has been caught. But people could have been. Two of the players were hit with them so whoever made the ridiculous decision, I don't think they will do it again."
Meanwhile, Birmingham opposite number Steve Cotterill said he felt the throwing of the clappers could have disrupted his side.
He added: "When they came on the pitch they might have hindered us as they slowed our momentum down.
"That is a decision the club will look at in the future, I am sure. All I would say is that when they came on they slowed our game down a little bit, which didn't help us."