The Football Association are investigating after Leeds fans hurled plastic flagsticks at an assistant referee during Garry Monk's tempestuous return to Elland Road.
A linesman sparked fury in the 77th minute of the Championship clash when he flagged a foul in the area which resulted in referee Keith Stroud awarding Monk's Middlesbrough a controversial penalty.
A number of flagsticks, ripped from flags handed out by Leeds to promote togetherness after a recent poor run before the game, were launched in the assistant referee's direction and there was a delay before the spot kick could be taken.
Sportsmail understands the incident featured in Stroud's match report and that the FA have now asked Leeds for their observations.