Wakefield Trinity Wildcats said they are “appalled” by fans who threw flares onto the pitch during their match at Castleford Tigers.
A smoke bomb disrupted play at the Mend-A-Hose Jungle stadium after Paul McShane scored for the Wildcats.
Wildcats chairman Michael Carter rushed over to the travelling supporters to try and find those responsible.
But a second flare was then thrown from the crowd onto the pitch.
The Wildcats, Castleford Tigers and the RFL have now launched an investigation into the incident.
A Wildcats spokesman said: “We would like to express extreme disappointment at the actions of the supporters who tarnished the image of the club on Sunday.
“The 1,500 or more travelling supporters behaved impeccably throughout the game but were let down by the actions of a small number of individuals who, if identified, will be banned from the club, ground and with the will of other parties, the sport of Rugby League, throughout the world.”
Mr Carter said he was appalled by the actions of a minority of fans and urged supporters to help identify those responsible.
Anyone with information should call the club on 01924 211 611 or email firstname.lastname@example.org.