Birmingham City was fined £42,500 by the Football Association (FA) after Jack Grealish was attacked by a fan during the derby clash with Aston Villa in March.
Grealish was punched by a supporter, who was later sentenced to 14 weeks in prison and handed a 10-year ban from football matches, as Villa beat Birmingham in the Championship en route to promotion.
Birmingham issued Grealish an apology and banned the perpetrator for life, with the FA now confirming the club's punishment over the incident.
"An independent regulatory commission has fined Birmingham City £42,500 and warned them as to their future conduct," said the FA's statement.
"The club submitted it used all due diligence but was found to have failed to ensure that its spectator[s], and all persons purporting to be its supporters or followers, conducted themselves in an orderly fashion and/or refrained from improper and/or violent behaviour and/or refrained from encroaching onto the pitch area during the EFL Championship fixture against Aston Villa on 10 March 2019."